Author Topic: Modifications Marauder Bullpup.  (Read 8322 times)

Offline Novagun

  • Moderator
  • Hero Member
  • *
  • Posts: 885
  • Mana -8
    • View Profile
Modifications Marauder Bullpup.
« on: July 14, 2013, 07:47:43 AM »
This modification is more of a rebuild of the rifle. It was done by a very skilled craftsaman and would be beyond the talents of most air rifle shooters. The end product is the result of many hours of careful planning and skilled work.

It started with a concept drawing of the .25 calibre the Benjamin Marauder Rifle as it would look straight from the shop and as it would be after modification.

The Modifications include:

*New Bullpup walnut stock
*Shortened barrel (3")
*New larger diameter shroud with Improved baffles and suppression
*New trigger and linkage
*CNC scope forward mount
*Single shot tray

The process has been recorded to form a project guide for anyone capable of doing such work. To pay a machinist to do the work for home assembly would be an expensive undertaking.

As it happened the modifications evolved as the job progressed but every step was measured and recorded. A certain amount of artistic licence was allowed to make a one off "art work."

The maker considers that the design including the stock could have been done on a CAD facility and converted to a DXF file and the fabrication done with CNC tooling. That is for the experts.
This method could do the job in half the time it took to do it all by hand to higher precision. 

The piccatinny riser mount was the most expensive part at $145, it is made by Steyr but could have been made. Other costs were:

Walnut slab: approx $35 (only used about a third of it)
Recoil pad: $30
Sandpaper and flapper wheels etc: $25
Cap screws grub screws and a selection of other hardware $12
New seals throughout, (bought 3 spares of everything): $14

A plan was roughed out  to make the scope mount and forward trigger group unit out of a 30mm block of 6061 T6 alloy. That required a considerable amount of work on a mill.
The  pressure gauge will be nicely recessed up under the stock in the thumb hole cut out area.

The BSA Lonestar barrel that was fitted to this rifle was already a few inches shorter than the original made by Green Mountain Barrels in the United States of America  so there was no need to shorten it any further. There is plenty of room for the new suppressor baffles.

The new BSA Lonestar barrel had a little more diameter than the original Green Mountain barrel so it was turned down to 1/2" to take the rear suppressor locating bush.
The bush also acted as a depth stopper when fitting the barrel so something needed to take its place when removed. This left an ugly step in the barrel. A press fit blind fit spacer tube was turned to the same diameter as the barrel and set up the correct length for the depth stop. With a little bit of bluing it looked like it was never there.

Next thing done was the new single shot adaptor to manually feed those giant pellets.
Some precision measurements were taken to prevent any feeding or rubbing problems.
The adaptor was milled ouy of 6061 t6 alloy.
With a bit of matt black anodizing along with the rest if the new shiny parts it will do the trick.

Here it is all fitted up and working perfectly!
At the same time the transfer port seals between the main valve and the barrel port were replaced while  the barrel was off.

The forming of the scope and forward trigger group mount were started.



The trigger assembly was striped and  the safety catch removed as there was no need for it and it gets in the way of the new trigger connecting rod. A decision had to be made whether to attach the new "pusher" connecting rod to the existing trigger like most modifications to the trigger lever or make a "reverse pull" one with the connecting rod entering through a new hole in the front of the trigger group. In order that the rifle could be returned to its standard stock if desired the first option would be less intrusive but the second option will make for easier stock in-letting and probably a better feeling more adjustable trigger.

The decision was not to modify the rifle in any way that wasn't reversible so a pusher extension linkage with adjustable length was the decision.XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
A pivot point block to slip on the trigger held in place with a grub screw was made: the length is adjustable on the stainless steel rod with locking nuts at both ends and allows fine adjstment of the trigger.


The trigger will be mounted to a block attached between the scope mounts like this..xxxxxxxxxxxxxx

A new larger diameter suppressor incorporating a one piece baffle system was turned on a lathe. The outer tube will slide over the barrel with the rear locating bush/seal grub screwed to the barrel like the original;
The baffle unit will screw on and lock it all into place. It is a very light weight suppressor weighing just under 100 grams! The air flow test was impressive.
The bottom picture is of the the new larger volume suppressor tubing next to the factory shroud. It is hard to tell but the new tube is a larger diameter; the old shroud actually fits neatly inside the new tubing.


The new suppressor is finished apart from a couple of  rubber 'O' rings and some grub screws to locate the rear bush.
The main body tube was turned down to just clear the air cylinder when fitted so the barrel remains  free floating.
Weighs 95 grams in total. The original factory suppressor weighed 185 grams.

As the factory barrel band was not used a new spacer for the front of the cylinder was turned out of a piece of 1 1/4" alloy solid bar. It has tidied that area up nicely.

The scope mounts were polished inside the cylinder holes and they slip on nicely.

Next came the stock.


« Last Edit: July 20, 2013, 11:11:06 PM by Novagun »


  • Guest
Re: Modifications Marauder Bullpup.
« Reply #1 on: July 14, 2013, 10:57:24 AM »
With most of the engineering part finished I've turned my attention to the stock.
I spent about an hour moving the template around the slab trying to envision the finished stock... happy with the piece but wont really see the true grain until I start the shaping. I should have taken a pic of the vast array of router guides and jigging I had set up to get the inletting right, It looked awkward to put it best.. This is my first stock Ive made by hand that is not to be a painted finish so Ive been sooooo careful not to slip with any power tools..
that said there's a lot of work to do on it yet so if you see a sudden shift from the idea of polished walnut to a nice olive drab paint job, you can assume Ive muffed it up and had to bog something :rolleyes:

<a href="" title="IMG_0985 (Small) by wingman177, on Flickr"><img src="" width="319" height="480" alt="IMG_0985 (Small)"></a> 

I spent about an hour behind the router tonight snorting sawdust and reminiscing my college wood working class...
I made a good start on the inletting. Nice snug fit too.


This is what happens when a M-Rod (rifle) and a P-Rod (pistol) get together....

The B-Rod (bullpup)...  yup it officially has a new name...

The scary inletting job is all done, it was a little more complex than I first thought so I'm very relieved to have that stage finished..

<a href="" title="IMG_1549 (Small) by wingman177, on Flickr"><img src="" width="360" height="480" alt="IMG_1549 (Small)"></a> 

<a href="" title="IMG_1532 (Small) by wingman177, on Flickr"><img src="" width="500" height="375" alt="IMG_1532 (Small)"></a>

Another couple of hours behind the router and its starting to take shape..
I had to shift the lateral router line down about 10mm due to the thin wood in the scope mount recesses. I wanted to be well clear so not to
 weaken it or in case they "broke through". It hasn't really changed the look to the original design though, they still look good.
I really wanted to stray away from the "chunky" looking bullpup designs commonly seen and endeavour to produce a thinner, slick, light weight
and more ergonomic stock.

<a href="" title="IMG_1536 (Small) by wingman177, on Flickr"><img src="" width="360" height="480" alt="IMG_1536 (Small)"></a> 

<a href="" title="IMG_1540 (Small) by wingman177, on Flickr"><img src="" width="500" height="375" alt="IMG_1540 (Small)"></a>

<a href="" title="IMG_1547 (Small) by wingman177, on Flickr"><img src="" width="500" height="375" alt="IMG_1547 (Small)"></a>

I finished cutting the basic outline now and have started roughing out the contours.. Its starting to show some really nice grain now..



I've got it all shaped out now which only leaves the sanding part... lots and lots of sanding!
I'm really loving the lines of this stock, the grain follows the curves just as I hoped it would when
I laid out the template. I have tried to keep the Eastern European stile lines which I'm quite fond of.
Probably not every bodies cup of tea.. but then again nor are bullpups



I found another air leak due to a damaged barrel seal. The bolt has taken chunks out of it causing fluctuating velocities
over the chrono. I replaced it with a Poly 90 "O" ring which are much harder wearing and less likely to catch on the bolt and cut. Problem gone :)

Couldn't help myself... I put it all together for a sneak preview of how it feels and handles... 
Here's a pic of the B-Rod next to the Steyr for a size comparison, the barrel lengths are the same on both rifles.
Total length of only 700mm, thats 45mm shorter than the std Edgun Matador.

I simply had to test the B-Rod before finishing the stock and sending all the alloy bits to the electro platers to be anodized matt black.. It shoulders really nicely and the weight and balance is nothing short of superb! Very very easy to hold steady while standing, its going to be a great hunting rifle for sure. The trigger is very crisp and as I had hoped feels like any other regular adjustable trigger


The B-Rod got some attention this arvo.. sat out in the sun with my wife with a glass of wine and got to work sanding the stock.(Now that's "Quality time") One of my pet ducks showed up to provide the entertainment.. very hard case bird with a real personality! Follows me every where.. even hunting.. have to keep the house doors shut or he comes in to hang out..

I have sanded all the orbital marks and router burns out and worked the stock down to P120 grit. The worst part is done.. just got to work my way down through the grades now. I  have wet it down with a wet rag and will let it dry over night, this raises all the loose wood fibres so they can be sanded off leaving a very good finish. I will do this with every step in paper grade until the final polish with steel wool and application of multiple coats of oil.


The pics below taken with a macro lens is the result of wetting the stock and drying it over night..
All the tiny broken fibres lift there heads for me to sand off making for a baby bum smooth finish and adds to the depth you can achieve when oiling timber.


I had a lazy night tonight and took a rest from sanding.. Instead I drilled the stock mounting hole and made the trigger guard.
With the original stock mounting bolt now being to far towards the rear, the need arises for a new stock fixing screw. I have incorporated the new mounting screw with trigger guard bolt. I manufactured the alloy trigger guard in a soft smooth curve to follow the lines of the stock and  it will be anodized black with the rest of the new alloy parts... please ignore the big ass s/s cap screw I have holding it on for the pic, It will be replaced with a nice flush mount black countersunk 1/4'' cap screw on final assembly. The bolt threads into the base of the front scope mounting block (strategically designed directly over the trigger guard mounting bolt) and locks the action/cylinder securely into the timber. The trigger guard was recessed flush with the stock very carefully by hand with a chisel and hammer, in hindsight I should have done this near the beginning with the router while I still had square edges to work with. No probs though, disaster averted and no nervous slips with the chisel this time round :) Hopefully tomorrow brings the enthusiasm to finish sanding the stock start the oiling process.

well I did it.. got that job out of the way.. first sealing coat of oil on.
I'll take some better pics tomorrow in the sunlight.. stunning piece of timber!


A total of 20 hours work and the stock is finished just applied the final coat of oil.



I have just fitted the recoil pad and weighed the stock, 980 grams.. the original Crossman stock weighs 1.450 kg so another weight savings on that one.


After another pre-fit in the stock I have decided to mod the trigger slightly,
I previously had just drilled small pilot holes for testing and was testing it with some small pivot bolts which worked satisfactory but I have decided to use an 1/8" roll pin as the main trigger pivot point so I've added a larger 1/4" diameter rolling brass bush through the top of the trigger so the alloy trigger isn't wearing on the split in the roll pin. With a little graphite grease on final assembly is will be far smoother with a zero play super slick "roller bearing" feel to it. The trigger slot needed widening slightly to accommodate the new brass bush and now has a couple of machined shim washers to take up the end play. I have also decided to mount the trigger block on the front scope mount block only, trimming off a bit more fat and loosing a few more grams. It was a bit over engineered to start with I think.


Originally I was going to remove the pressure gauge and just blank it off but decided to leave it and make it visible through a porthole in the underside of the stock. Glad I did, Its made quite a cool feature out of it I think.

On the home straight now.. just got to drill and tap a few holes for the trigger to mount and polish all the machine marks out of the alloy bits to be sent away to the electro platers this week.


I finished all the final fitting of the trigger group today, I had to go with some very small 3mm cap screws to go through
the front mount to straddle the stock mounting bolt, tapping the tiny 3mm threads while the tap twisted and creaked through
the very hard aircraft alloy, It was a little nerve racking but no issues, I didn't break it and it all fits up nice and square.


Another pre-fit with the new stock countersunk cap screw and its all sitting perfectly in place. I made a small guide for the rear of the trigger conrod that mounts to the old stock mounting hole with a shorter cap screw to keep every thing running square and smooth. Also turned a 4mm stainless steel pin for the trigger to conrod pivot, also fine tuned the rod length and trigger position. The trigger is silky smooth now and you couldn't tell the difference between pulling the front trigger to pulling the std rear trigger.



Here's all the new parts polished and ready to anodize. They collectively weigh 440 grams
Which means I have added 12 new components and the new stock to this rifle and it is still lighter
than the std factory rifle, pretty happy with that :)


  • Guest
Re: Modifications Marauder Bullpup.
« Reply #2 on: July 14, 2013, 11:01:32 AM »
With all the bits polished and off to the electro platers tomorrow, I turned my attention to the accuracy issues this rifle was suffering when I bought it.

The groups were very inconsistent with 3 different brands of pellets I tried.
Not surprisingly the wolverine 25.0gr pellets made for BSA by JSB were the best shooters but at 50m I had plenty of flyers.
When I removed the barrel to start this project I pushed a few pellets through it with my cleaning rod, all seems very good, a firm consistent bite the entire length until the last tighter 2 inches where the barrel is choked. I would go as far as saying this barrel is tight, not uncommon for BSA barrels Ive heard.

Something didn't sit right with me in regards to the bolt operation though..
It seemed to need far too much pressure to seat the pellet and lock the bolt closed. Tonight I looked at this a little closer by loading a pellet in then removing the barrel and pushing it back out the way it went it with my cleaning rod. The skirt was very damaged from the bolt and it had very uneven rifling grooves it the head, one side of the pellet they were cut deep and the other they were only very slight. 


I repeated the same task with the original Green mountain barrel fitted and there was no issue at all and very minimal pressure required to close the bolt. This tells me BSA have a much tighter chambering/leads. I'm unfamiliar with the BSA Lonestars bolt probe system but  its apparent that the Marauder is very different. Under closer inspection I found a very ugly chamber, the lead into the rifling lands was very lop sided, I would say as far as 2mm on one side, this explains the marks in the pellets heads and no doubt the cause of the poor accuracy. The uneven lands were acting like a feed ramp cocking the pellet to one side on entrance.
I had a measure up of the Green mountains chamber and compared it to the BSA barrel. The G/M measures 0.2600" (6.60mm) and the BSA was only .2534" (just over a 1/4 inch. Into the lathe it went.. I first opened it up with a 6.5mm (0.2560") drill and tried a pellet.. It was even worse! so tight it buggered the skirt..
now how could taking material out of the chamber make it worse I thought? what it had done in turn was create a steeper angle on the rifling lands making a sharper step for the pellet to enter.. sooo... next I used a letter F drill, (.2570" or 6.53mm) still not quite the 0.2600" (6.60mm) of the G/M but thats the closest I had, and the next size up is a letter G drill, just a tad too big at 0.2610" (6.62mm)
After running the F drill through it and pushing the lands back to the same depth as the G/M barrel I trailed another pellet. This time It was much better but it still had the sharp step onto the lands the require a little more bolt pressure than I would like so I ground a very large taper into the end of my F drill and gave the lands a light touch with that and gave the chamber a quick polish.. The end result is very pleasing, the pellet slips in with nice even bolt pressure all the way to lock up and now has nice neat even rifling cuts around the head.

Heres a photo of before and after.. Probably should have cleaned out the dust for the pic..

I also noticed the crown was very ugly and it had an off centre countersunk section, Hard to see in the photo but that certainly wasn't aiding accuracy..
Back on the lathe I cut one of my favourite target crowns.. a square cut crown with an 11 degree target recess, mainly because its pretty but also very functional.
Hopefully once its all back in one piece with this barrel work done along with all the replaced seals this little pup will stack pellets with the best of them.. time will tell...:rolleyes:



With the B-Rod build nearing completion only awaiting the return of the newly anodized parts and final assembly, the hunt for the perfect .25 cal pellet to short BSA barrel marriage starts….

Instead of using 10 different pellets and the related ideal velocities for each, the Marauder is to be set at the best velocity for the best pellet. In the coming weeks, I'll share my experience in determining that pellet and touch on rifle tuning techniques.

Unlike my Steyr the Maurauder is unregulated meaning the velocity and cylinder pressure work independently
If either one of these variables changes, the other will also change. When setting a non regulated rifle up, you have to find a balance between both variables. It isn't difficult to do, but it's a complex relationship. A chronograph is defiantly needed to adjust the velocity.
There are 3 main adjustable components on the B-Rods air system:
The velocity metering screw (opens and closes the port into the barrel), the striker pin valve travel and the hammer spring preload.

Ideally I want a heavy pellet 28-40gr with a minimum of 50ftlbs,
I intend to use the B-Rod for short range goats and long range rabbits just how “long range” will be determined by the capabilities of the selected pellet not the rifle I'm guessing..
The pellet needs carry plenty of energy short range and be very accurate at the longer ranges so I'm focussing my testing on proven dome head pellets with the higher B C.
Like my Steyr I'm going to run the bullpup very hot to get the most energy the .25cal has to offer, an accurate flatter flying pellet is more important than shot count for me.
I have no interest in the gimmicky hollow points or pointed pellets as the expansion on the hollows is very marginal and the B C’s suffer on both types limiting their long range capabilities.  I do however have a part tin of H&N hollow point that came with the rifle when I bought it so I will add them to the list for interest’s sakes only.

I have spent quite a few hours searching for info on the net for related .25cal ballistics and found very little facts on many of the pellets that I will test.
There was some good info on heavy cast bullets also Eunjin 35.8 and 43.0gr pellets seemed to be favoured in the states but neither of these seem to be overly accurate or available here in NZ. I found some on eBay for 8 pounds and 2 pounds postage but I just can’t seem to bring myself to import and shoot Korean made pellets no matter how cheap they are.

One pellet that did get my attention was the Daystate Rangemaster 36.0gr pellet, this one ticks all the boxes for me but they were unavailable unless I imported them myself…

So I Did… :rolleyes: I cant wait for that package to turn up.. 

The first thing I noticed while purchasing test pellets was the very limited range and stock of .25 pellets available in comparison with .177 and .22 pellets. Some gun stores didn't even know what they were and tried selling me .22 pellets as they were sure I had made a mistake.. They also seemed to lean towards the light weight side of pellets. However… I have imported some myself and I rang retailers from one end of the country to the other and scratched together 11 different hopefuls:

JSB Exact Kings 25.4gr
H&N Field Target Trophy 20.06gr
BSA Wolverines 25.0gr
H&N Barracuda ‘AKA’ Beeman Kodiaks 31.02gr
Benjamin Premiers 27.8gr
RWS Super Domes 31.0gr
H&N Hollow Points 26.23gr
Predator Bigboy Senior 31.0gr
Gamo Hunter 21.6gr
Daystate Rangemaster 36.0gr
I will start by shooting all of these pellets with the gun set on the “Maxed the fk out” settings, pushing them as hot as they will go to see if any of them will group..
From there I will fine tune the hopefuls.
I will review each pellet in depth as I go and with any luck get this M-pup shooting inside the inch at 100 meters

All the parts are back and black, I will assemble and post picks tomorrow..
For now here's some info on the current state of tune..

The valve
The most commonly used air valve in airguns today is the knock-open valve. To operate it, a valve stem is struck by the hammer that is driven by a spring. The inertia of the impact moves the valve stem in the same direction. There is a synthetic valve face on the valve stem that holds the high-pressure air (or CO2) inside a reservoir until the valve is open. A valve-return spring starts the valve moving back toward the closed position after the valve has opened as far as it can. Once the valve stem starts to return to the closed position, the pressure of the air or gas in the reservoir also pushes on it. That's because the pressure inside the channel of the valve body is always a little lower than the pressure in the reservoir. If it weren't, the valve would remain open longer, dumping a lot of the air in one shot. The little valve-return spring exerts a huge controlling force over the valve because of this pressure differential.

How the valve is designed and set up determines performance
You can affect how long a valve remains open by adjusting the strength of the return spring, the pressure inside the reservoir, the length of travel of the valve stem and the inertia of the hammer. The more dwell time the longer the valve remains open, the more air will flow through it.  There are limits, however, which is why you don't get an increase in power beyond a certain point when you install a heavier hammer or a stronger hammer spring.
I have replaced the factory 8 lb hammer spring with a 10.5 lb spring and set the dwell time on the valve striker pin to it shortest setting meaning its open for a shorter time. Fitting a spring to this rifle over 10.5lbs wont change anything it will only make it harder to cock. Some rifles will need a mod to the transfer port after a mod like this to cope with the shorter burst but greater volume of air but not the Marauder, it has an adjustable metering screw which opens and closes the transfer port. I have set this screw to the maximum open position.
The heavier spring also eliminates hammer bounce which waists a good 20% of the air in the factory settings with a weaker spring fitted.
With the mods I've done to this rifle I substituted dwell time for the extra pressure, to extract all the performance the air has to offer in a shorter time.

The secret with this guns inherent accuracy is a well-balanced valve that doesn't require raw pressure in order to function.
The Marauder is set to operate on a 3000 psi fill from the factory. I say that because the Marauder will function with any fill pressure from 2,000 to 3,000 psi — it’s adjustable by the owner. But the .25 screams to be set up for the full 3,000 psi. That’s because this big .25 is a real thumper that uses a lot of air for each shot.
However, while I was testing the gun on factory settings, I fired strings starting at a 3000 psi fill. In other words, I topped up the gun between each string. In doing so, I noted that the initial shots were lower in velocity, meaning that this particular rifle needs a fill of somewhat less than 3000 for optimal performance. It got 16 (two mags) very consistent shots between 2800psi and 1900psi before the pressure drops away rapidly. The factory set it up this way to get the highest shot count and smoothest shot curve possible. 
The mods I have made to the B-rod to make the most of its 3000psi fill but subsequently  have sacrificed shot count for velocity and consistency, in my application this is what I wanted.

Check out the curves below to see the results of the tune up.
The red line is factory setting and the green is after the tune.

Red * I shot strings from a 3000psi fill in the factory settings first, the 16 usable shots  between 2850psi and 1900psi over the chrony were as follows:
The pellets were Benjamin 27.8gr Premiers

773fps  796fps  802fps  798fps  784fps  793fps  811fps  801fps 821fps  826fps  829fps  805fps  821fps  817fps  802fps  789 fps

Average speed: 804fps
Average energy: 39.9 ftlbs
Extreme spread: 16fps
Standard deviation:15.7fps

Not bad for an entry level hunting rifle!

Green * The second shot string with the Benjamin 27.8gr Premiers
from a 3000psi fill to 2000psi is the 10 usable shots after the tune.
The chrony results were as follows:

958fps  957fps  955fps  956fps   957fps  952fps  948fps  946fps  945fps  942fps
Average speed: 951fps
Average energy: 55.9 ftlbs
Extreme spread: 16fps
Standard deviation: 5.8fps

Now those are the figures I was hoping for…  on to the pellet tests and groupings...

The parts are back and the anodizers did a perfect job for me as usual...

I fitted it all up with nice new cap screws, graphite grease on all the trigger mechanism  and silicon grease on all the new seals. Its all looking and operating so sweet..

Here's what you have all been waiting for...The Marauder bullpup "glamour shots"
It is one fantastic rifle for such a minimal cash outlay.



Here it is with some larger Falcon optics fitted, I decided it was just too much scope for the B-Rod, it added too much weight..
After a couple of sighters I gassed it up and emptied 2 mags of BSA wolverine pellets onto paper.. I must say I'm still grinning!
One ragged hole at 30m! Cant wait to trail the other pellets and stretch its legs a bit further!


  • Guest
Re: Modifications Marauder Bullpup.
« Reply #3 on: July 14, 2013, 11:03:35 AM »
I should start with the same declaration I started with in my Steyr v/s .177pellet review:

My writings are strictly my personal opinions and findings and should be treated as such.

There is no “one” perfect pellet that will shoot perfectly in every body’s rifle; this is the hunt to find a pellet for mine.
Personal results will vary hugely depending on pellet, batch, size, shape and length v/s velocity, rifle setup/characteristics, bore size, barrel length and twist rate.

I am not a bench rest or F/T shooter and don’t care for shooting paper for any other reason than sighting in. I use my rifles solely for pest control and rely on very accurate combos for long range humane kills.

A heavy domed or round-nose pellet was the basis of my search as they have the best ballistic coefficients and have more of a chance achieving my end goal with the bullpup.
Currently on  my desk is a pile different .25 cal pellet tins...


In this stack of tins, I can tell you that there isn’t one true premium heavy .25 cal pellet that is readily available in NZ. I’m faced, instead, with using the best I could  find and awaiting a couple of imports, I will probably subside to importing them myself should my findings point in any other direction than the RWS, H&N’s or JSBs which seem to be the only pellet brands stocked by NZ dealers with any regularity.
The JSBs and H&N FTT have a good rep for shooting well in most rifles but at 25.4gr and 20.06gr it’s a bit on the light side for what I’m looking for. However they will be something to fall back on should the heavies not perform.
The H&N Barracuda heavy 31.02gr pellets in my opinion are restricted by design, they have a very thick skirt and a semi pointed dome tending towards short range accuracy and penetration. Lets hope I’m wrong with that because they are the cheapest heavy pellet and easiest for me to obtain.

Already one pellet stands out from the rest… the Benjamin Premiers.
The Benjamin pellet is, without a doubt, a Crosman Premier by another name,
I found an article on the web that stated Ed Schultz at Crosman took their best ballistic coefficient Premier,
which ironically turned out to be the .20 cal, and stretched it out to .25.
It also looks remarkably like the .177 10.5gr premier scaled up. Here they are side by side…


The Crosman pellets come 200 to a large tin with a screw top. That screw top is a feature all by itself.. Nothing worse than an open tin of pellets in your range bag or a clumsy
opening slip top scattering pellets from here to next week, these tins prevent that annoying mishap.
My plan is to test the heck out of this pellet, as its design proved itself effortlessly at high speed and long ranges in my Steyr so there is a good chance it will do the same in my Bullpup.
I don’t mean to denigrate the other .25 cal. pellets by gushing over this one, this is just where I started with a quick visual inspection and measure up, and in my mind they are once again... the benchmark.

The line up with factory listed weights:

#1: H&N Field Target Trophy 20.06gr
#2: H&N Barracuda 31.06gr
#3: Gamo Hunter 21.6gr
#4: RWS Superdome 31.0gr
#5: JSB Diabolo King 25.4gr
#6: Daystate Rangemaster 36.0gr
#7: Benjamin Premier 27.8gr
#8: Predator Pollymag 26gr
#9: BSA Wolverine 25.0gr
#10: Predator Bigboy Senior 31.0gr
#11: H&N Hollow Point 26.23gr

The test:
I have given the bore a really good scrub and run patches till it was completely clean.. I have since fired about 100 shots through it to get familiar with the rifle and “season” the bore. I have to say Im really liking the new bullpup! It is so well balanced and an absolute pleasure to shoot. The lighter .25cal pellets scream out at over 1000fps with quite a crack and the trajectory is better than I had expected, the heavier pellet however have a satisfying thud report with a smooth but exciting recoil.. at the receiving end, an echoing thump of authority can be heard as the .25 cal energy demonstrates its capabilities on whatever it hits..

I decided to use the magazine for this test rather than the singe shot tray as this is a hunting rifle, and it should be able to feed the chosen pellets should I choose to use it at any time. There absolutely no feeding issues with my newly machined chamber and no damaged caused to any pellet skirts by the bolt so there is no reason why the magazine will affect accuracy during the trials. 
The pellet testing was done as follows: I filled the cylinder to 3000psi for each brand. The mag holds 8 pellets so the mag was filled with the individual brand being tested, the first 3 shots were fired on the sighter board (whether they were needed or not) and the remaining 5 were shot on the individual ½” bullseye targets.
All these pellets were tested consecutively late in the evening on the same day without wind and at the range of 50 meters.
This was an out of the tin test, so no sorting, weighing, lube or grading of any sort before they were tested. The rifle is shot while “floated on a bench rest and only the trigger touched to remove 99% of human error.
The first 8 pellets Ive tested show me that this rifle is really not that pellet fussy… its shot nearly all the brands under an inch at 50 meters, some however inside half an inch! That’s accuracy outstanding for a non regulated rifle in my opinion!

Here’s how the first 8 brands “stacked up”…


H&N Hollow Point

Weight: 26.23gr
Head diameter: 6.34mm
Skirt diameter: 6.42mm
Average velocity: 965 fps
Average energy: 54.25 ft lbs

I didn’t spent too much time trailing this German made pellet as I pointed out in an earlier post; a Hollow point is not what I am after but I had some so have included it in this test. It shot well in my opinion well under the inch at 50m.
Here’s what the manufactures had to say about it:
This hollow point is a lightweight, accurate pellet with flat trajectory for medium ranges. It imparts maximum shock effect and with higher powered guns for even deformation of the pellet. It great for universal use

Out of interest I have shot one of these through some ballistic gel to test its mushrooming capabilities which to me seem poor at best. The pellet in the pic was shot at approx 965fps at about 1 meter away.


H&N Barracuda

Weight: 31.02
Head diameter: 6.35mm
Skirt diameter: 6.45mm
Average velocity: 945 fps
Average energy: 61.53 ft lbs

These pellets are also sold as Beeman Kodiaks.
Just bought a new 2012 batch of these pellets and was stoaked to see they are now sold in a tin with a screw top lid!
But that’s about where my excitement stops on these ones…
Like I said earlier these pellets are too pointed to be good long range pellets or even mid ranged seemed to be plagued with problematic flyers. Most of the pellets seem to group nicely and find the same ragged hole but there seems to be about 1 in 5 pellets that randomly head off on their own adventure.. It could be size or weight irregularities but still very odd, so I decide to test this pellet a bit further as I would like to give it a fair chance in the test.
I weighed a handful of the Barracudas and they ranged from 29.8 grains to 30.3 grains. That’s a very tight spread, but not as heavy as advertised (which is 31.02). The average weight for Barracudas was 30.0 grains so even though they were not as heavy as the tin said they were consistent and the weight is not the cause of the flyers.
Ten shots over the chrony the Barracudas ranged from a low of 939 fps to a high of 948fps. The average for this pellet was 945 fps, again no real issues there, the head diameters are very consistent 6.35 but the skirt diameters fluctuated a little mainly from tin damage (small flats) which is all I can point my finger at for now. I will mount the scope cam on the bullpup and shoot some of these pellets out a bit further, then watch the slow motion playback for instability issues typical of pointed pellets. Short of that the flyers are a mystery???


Benjamin Premiers

Weight: 27.8gr
Head diameter: 6.35mm
Skirt diameter: 6.45mm
Average velocity: 951 fps
Average energy: 55.9 ft lbs

Once again Crosman showing us that they consistently produce the best pellets in the world!
What can I say? A single hole with 5 pellets stacked end on end!
Now that’s what I was hoping to see from these pellets.
Interestingly enough they share the same head and skirt dimensions of the Barracudas but are drastically different by design. I weighed a handful of Benjamins and this group ranged from 27.3 to 27.9 grains, another very tight spread. The average was 27.6 grains. You can see the chrony shot spread and shot curve for this pellet few posts back
I can’t wait to see what this pellet is capable of once sorted lubed and sent out to much longer ranges!
Two things id like for this pellet is a heavy weight version and better availability… any one know if this pellet is being imported by any NZ dealers?
One pellet not in my test is the Webly Accupells, they are the same pellet as these I believe, but not tined in single die batches so weights and head sizes will vary I’m sure.


Predator Big Boy Senior

Weight: 31.0gr
Head diameter: 6.36mm
Skirt diameter: 6.45mm
Average velocity: 947 fps
Average energy: 61.75ft lbs

These pellets are made in Hungary by Skenco, the same factory that brings us Predator Pollymags. These pellets I refer to as JSB heavies for lack of a better description.
It wouldn’t surprise me if JSB start to make these under contract like the Polymags and offer them along side the JSB Kings as a heavy option
They are expensive at $15 for 90 Pellets packed in a plastic container with foam on the top and bottom.
They are however well made and very consistent, they are very much like the H&N Barracudas by design and weight but have more of a dome head and sharper edges typical of the JSB Diabolo designs.
I nearly forgot the best part… the B-Rod loves them! A nice group of less than ½ an inch..


RWS Superdome

Weight: 31.0gr
Head diameter: 6.30mm
Skirt diameter: 6.45mm
Average velocity: 952 fps
Average energy: 62.4 ft lbs

Once again German made RWS make a lovely shiny smooth pellet with next to no imperfections. The weight and velocities were very consistent. The velocities were very high as was their point of impact so I put this lousy 2 ½” group down to head size. The head size on these pellets are very small at only 6.30mm, BSA barrels are known to be some of the tightest by nature so I’m not sure what market these pellets are aimed at? Possibly 12ftlb pcps or lesser powered spring guns?
It’s a shame because the pellet design is very good and I have no doubt they would perform had the head size been 6.35-6.37mm.



  • Guest
Re: Modifications Marauder Bullpup.
« Reply #4 on: July 14, 2013, 11:05:15 AM »
H&N Field Target Trophy

Weight: 20.06gr
Head diameter: 6.37mm
Skirt diameter: 6.52mm
Average velocity: 1002 fps
Average energy: 44.73ft lbs

These numbers alone don’t impress me on these pellets, the lighter weight drags the energy rating down dramatically to the point that I may as well be using a .22cal to get that energy rather than the .25cal. Again with the H&N pellets I got plenty of flyers.. Speed could be an issue here but without this speed these pellets have no use to me at all. A very well made pellet again and very similar to the JSB Kings to look at with the nice sharp waist lines and dome heads. Again I weighed a handful and got a range from 18.9gr to 19.7gr, and again much lighter than the advertised average of 20.06gr. I am fast Going off H&N pellets and German pellets in general. A positive note though these were VERY flat shooters! Impressive for a .25 cal.. now if only they would group…


BSA Wolverine
Weight: 25.4gr
Head diameter: 6.35mm
Skirt diameter: 6.58mm
Average velocity: 971 fps
Average energy: 53.1 ft lbs

I believe these pellets Are no longer made but I same story.. I have some so I’ll test them.
These pellets were made for BSA in Czech Republic by JSB and look in every way like the .25 cal JSB Kings. As soon as my JSB pellets arrive I will confirm this suspicion that they are indeed the same pellet. Im kind of hoping they are because they will be my “go to” light weight plinking pellet.
They are a little on the light side for long range energy delivery but make for some good shorter range plinking and accurate enough to take out larger birds past the 50 meter mark.. Go on… ask me how I know this… :)
The skirt diameter is slightly larger on these to the other pellets tested and the have a nice snug fit to the chamber. Great result at 50m with a nice tight ragged group equal to the Predator Big Boy pellets


Gamo Hunter

Weight: 21.6gr
Head diameter: 6.27mm to 6.37mm
Skirt diameter: 6.27mm to 6.77mm
Average velocity: 996 fps
Average energy: 47.59 ft lbs

Once again the Spanish wild card… These pellets were $15 for 200 so I thought why not? When I opened the tin I held back the laughter and began to search for some pellets that looked like… well….. pellets…
Again I shot this group from right out of the tin without sorting other than a close visual to make sure they were round and didn’t have any wild lead sculptures hanging off their extremities… these pellets have a massive fluctuation in head and skirt sizes and weights to match but just look at that group!!! I did say the Bullpup wasn’t fussy didn’t I?
Im picking If you have the time and equipment to sort these pellets you may get 40-50 good ones out of 200 from a tin but that’s a silly Spanish game I don’t wish to play.. certainly not at $15 for maybe 50 pellets anyway…
Heres a close up of some of Gamos fine art works included in every tin…


Daystate Rangemaster

Weight: 36.2gr
Head diameter: 6.37mm
Skirt diameter: 6.55mm
Average velocity: 934 fps
Average energy: 70.14 ft lbs

My Daystate Rangemaster twenty fives arrived today from the UK so I been testing them with great interest all afternoon. These pellets are very long but still fit in the modest marauder magazine. These were specifically designed to shoot well in the .25 cal Daystate Air Ranger 80.
This unique pellet design is very well known for their wind bucking abilities with supreme penetrating capabilities and retaining considerably more energy than other pellets in its class. It is what I would call a true heavy weight .25cal pellet. The first interesting point I noticed was on the side of the box... It reads: Will perform best in high power airguns fitted with a .25 inch (6.35 mm) unchoked barrels! This I find a bit weird since these are advertised as best for the Air Ranger 80 ft/lb which is by the way choked..
Well my barrel is as tight as they come and is choked so that will be interesting test... the measure up tells me the heads ware 6.37mm so on a par with the H&N FTT pellets. They state a pellet weight of 36.0gr on the box but all I have weighed are 36.22gr-36.28gr so a nice bonus there. The differentiating factor of these pellets though are in the design, they have a very shallow skirt, forward COG and very minimal bore contact on both skirt and head contact points, this was evident over the chrony with an average velocity of a rip snorting 934fps! That is only about 20fps slower than the 28-30gr pellets! That speed and weight equates to a massive 70 ftlb of muzzle energy which I cant wait to test on soft targets :) The big advantage here is the BC. Because they are virtually solid the longer range energy is so much greater (maybe 40% more) than Cudas, etc.
After shooting plenty of these pellets in the windy conditions that today brought me I figured I'd putt them on paper to see how they perform...
I shot this group at 50m in fair to light wind with a minor correction for windage dialled in.. this was the best of 3 groups I shot with the others displaying slight lateral flyers in the direction of the wind gusts. (to be expected)
Ill give these another go when conditions are still again but have all the confidence in them that the groups will only improve.
I think I have found a Heavy weight competitor for the Predator Big Boys and the Benjamin Premiers for an accurate long range pellet...



Weight: 25.4gr
Head diameter: 6.35mm
Skirt diameter: 6.58mm
Average velocity: 968 fps
Average energy: 52.8 ft lbs

I finally got to test some JSB kings along side the BSA Wolverines and it looks like my suspicions were correct, they are indeed the same pellet.
The same dimensions and weight although on the wolverine box it states 25.0gr not 25.4gr but they do actually weigh 25.4gr.
Not surprisingly they shot the same tight group at 50 meters as the Wolverines did too.
As I said in my BSA review these pellets are a bit on the light side for long range work but make for good shorter range plinking.

I thought rather than a boring review of the same pellet I'd add a scope cam vid of a group, this proved harder than it sounds as
the light was fading and the scope cam is hard to use at the best of time so I shot one at 30 meters so the impacts were more visible....

Marauder Bullpup 30 Meter groups with JSB 25.4gr Kings

Predator Polymag

Weight: 26.0gr
Head diameter: 6.36mm
Skirt diameter: 6.65mm
Average velocity: 962 fps
Average energy: 53.4 ft lbs

I know I know.. I said I wouldn't be testing the hollow points and gimmicky pellets but I couldn't help myself with these ones as they did so well out to 50m in the .177 Steyr..
These Pellets are sold through the USA owned Predator International Inc but the lead is put through the die in Czech Republic by JSB then sent to Hungary to be assembled with the tip and tinned at a 150 count.
They are packed very tightly between foam in the tin but there is still a very high number of pellets with flat spots on the skirts.. possibly from the added amounts of handling in the production of this complex little pellet.
The tin states: " Match grade accuracy with incomparable penetration and expansion"
Im not sure if that means there is no other similar pellet you can compare the penetration and expansion to or it simply out performs every other pellet in both these attributes??? Either way I was going to try..
In my .177 reviews  I tested the Fireball pellet which also made this claim.. this is my school of thought on this matter: I may not be a ballistics expert, but I am both a shooter and a hand loader who knows that penetration and shock are at opposite ends of the performance spectrum. They are directly linked, as in "greater penetration equals less shock. For penetration, a projectile has to retain energy as long as possible, carrying it deep into the target. To generate shock, a projectile must transfer energy as fast as possible to the target. These are mutually exclusive goals, and my guess basing it on my .177 polymag tests is they would excel in expansion and fall short in penetration.. 
These pellets however are a bit more solidly made than the .177s and their expansion capabilities were not as good in the ballistic gel test.
I saved the ballistic gel from my last tests by reheating it and storing it in 3ltr bottles... instead of remoulding it I just shot through the cap of the bottle which did contain a bit of the energy release as you can see in the video below.. The pellet stopped at 195mm into the gel, the tip was found at 80mm in. I shot a 25.4 Gr JSB king  into the gel too as it is a similar weight and it went  right through the gel exiting the bottom of the plastic and embedding itself into the tree behind.. so the penetration was defiantly less than that of a similar weight pellet and the expansion was fair to average and Id say no better than the hollow point H&N Which stopped when it hit the bottom of the bottle (260mm of gel) but still a good close range hunting pellet for rabbits and possums etc. The price difference over a good quality dome pellet to me renders them just another gimmick with debatable advantages, the standard dome pellet already shows signs of excessive energy on the smaller game with the .25 cal.
They did however group very well at 50 meters but Im sure things will change dramatically at the 100 meter tests as they did in the .177 tests.
It pays not to think about the $39 for 150 you will part with for a tin of these especially when a $14 for 200 Gamo Hunters shot about the same sized group in the bullpup!


I removed the ballistic gel from the plastic bottle and decided to put another Polymag into it without the constriction of the bottle and the cap to shoot through and the results were very different....
The pellet expanded twice as much and only penetrated 125mm of gel..
The cap must have taken some energy from the first test causing the pellet to burrow deeper and restricting expansion. This is more what Id expect from a pellet like this, a far more impressive result. 
I guess in its real world use the expansion will depend a lot on what its passing through.. bone would be an interesting one..

here they are side by side:


The urge to test an even heavier pellet is returning... maybe a solid cast bullet or a 43.0gr EunJin pellet or some of the 43-50gr Mr H/P cast bullets..


Ok maybe not the EunJin korean crap but something heavy.
Already I have dispatched mynahs and starlings with the Benjamin Prems out past 150 meters with surgical like precision so I look forward to testing them on paper at the longer ranges.
I will test the best of the pellets trailed out to 250 meters when the weather permits.



  • Guest
Re: Modifications Marauder Bullpup.
« Reply #5 on: July 14, 2013, 11:08:12 AM »
RCBS and LYMAN both make a mould that casts a 50gr .251 (6.37mm) bullet: but the .25acp bullets are not really the best design for an airgun. The contacting belts are to wide  and would make for too much friction dropping velocities and causing bore leading problems.. I think the best bet would be to custom design one to be made with very minimal surface area contacting the rifling (like a std pellet)
I wouldnt even try a .257 cal casting even if sized to .251 the issues mentioned above would be worse and like you say the bullets would be too long and heavy (100-130gr) for the twist rate and velocity achieved.

Out of interest I fitted an even heavier 18lb hammer spring today with thicker wire and a shorter compression length. I did this just to see the maximum capabilities of the Marauders valve without further mods like opening up the transfer port etc...
I put a few different pellets over the chrony with this set up and was shocked! My heaviest 36.2gr Daystate Rangemasters maxed a scorching 998fps! Thats just over 80 ftlbs!!! With a usable shot count of just 3 shots from 3000psi to 1900psi.. now that's hoggin some air! I would love to test a 50gr bullet at this setting..
The noise and recoil from this experiment was nothing short of harsh..
A short range head shot from a 50gr pellet with this setting would be a very capable pig, goat or dear stopper..

The top spring is the 18lb test spring, the middle one is my 10.5 tuned spring and the botom one is the factory std spring.


Here's a 100lb pig shot with a factory Marauder with a 27.8gr Benjamin pellet at about 40ftlb..Maybe a heavier pellet is totally unnecessary?


The bullpup stars in its first movie..

#4 Pest control with a .25 cal Marauder Bullpup PCP

The weather has been crap all week so long range testing is still on hold..
Im getting plenty of pest control trigger time on it though so all is not lost.
I actually haven't shot the Steyr since I finished the bullpup! Ive blowen through 2 dive bottles of air,
hundreds of pellets and the .25 critter count is growing daily.. roll on sunshine!

Well its still too windy to group the various pellet brands at the longer ranges but I did have a play at 120 meters
with some water balloons in the trees..
120 meter targets with the .25 cal Marauder Custom Bullpup

They are a good practice size close to a bird or possum/rabbits head size.
Taping paint balls to a board also works well for long range practice. Note how strong the wind is in this vid,
only a small windage correction was dialled in, the .25cal doesn't seem to be too affected by it compared to the .177

Finally got some good weather in the Waikato today so I spent a few hours grouping the various pellets at 100m, 150m, 200m and 250m..
the results were as follows:

100 Meters


150 Meters


250 Meters


They all did better than I had expected actually..  None really stood out over the others, there 5 brands of pellets here that Id be happy to shoot at short or long range. The Prems and JSB's are pretty much neck and neck, the JSB's are easier to get but the Prems carry a bit more energy being slightly heavier.
The Daystate Rangemaster 36gr heavies are expensive and have to be imported so Ill probably put this box aside for close range goats, pigs and maybe even a fallow deer if one should presented itself but not use them as an everyday "go to" pellet.
I wont be using the H&N as there are too many flyers or the Bigboys as they are just to expensive for an average shooting pellet.
The Pollymags defiantly performed better than I thought they would and will be good rabbit and possum pellets but realistically Id probably only shoot with them to about 80 meters.:rolleyes:

This test leaves me torn between the JSB Kings and the Benjamin Prems and unfortunately they both have a different P.O.I so I cant switch between the two without re-sighting. I suppose this situation is better than a pellet fussy rifle like my Steyr that only shoots one expensive hard to get brand..

Grouping your airgun; The profession of stacking pellets into single lumps of little lead art works

The .25cal is a bit hard on back stops too.. looks like Im going to need a new piece of 12" X 2"

With the conclusion of my testing and a fair bit of hunting the approximate pellet count is as follows:

JSB Kings: 300+
Benjamin Premiers: 430+
Daystate Rangemasters: 120+
an assortment of the other brands tested: 200+

The pellet count is now over 1000 rounds, so this afternoon I stripped the bullpup for its first service and thorough clean.

I first removed the breach 'O' ring and checked it for wear/damage...All looks good, the harder compound Polly 90 looks like its doing the job well.
Next I removed the suppressor for cleaning and inspection. The baffle design looks too be very efficient at not only reducing the muzzle blast but catching a very good percentage of the lead dust too...
Looking inside the suppressors main body tube you can see little mountains of lead deposits redirected by the baffle design also a lot of blow back deposited on the barrel itself.
When I assembled the rifle I coated all these parts in silicone grease to stop the parts seizing up and aid in easy cleaning further down the track..



Next I dragged a wet patch of bore solvent through from the breach end where I had removed the 'O' ring, (Note dont get bore solvents near your seals)
It was a tad dirty to say the least.. it has had a few dry patches through it but this is the first solvent clean its had since the build... 9 more dry patches later and the tube is 1/4 of an inch of twisted shining chrome! Now the bore is well run in/seasoned, I will wash and lube all pellets to be shot in it. 
I washed all the suppressor parts and outer barrel in white spirits and smeared them with a light coating of silicone grease before re-assembling them. The Breach seal got the same treatment with silicon grease and was reseated.
A small amount of graphite grease on the bolt cocking mechanism has smoothed up the action cocking too as it was starting to sound very dry. The blued metal work got a light coating of RemOil and finally I have given the stock another light coat of oil and the pup is set for another 1000 pellets at least.



I figured a few more Glamour shots would be the best way to wrap this thread up...



  • Guest
Re: Modifications Marauder Bullpup.
« Reply #6 on: July 14, 2013, 11:10:29 AM »
.25 cal Marauder Bullpup 100m group


  • Guest
Re: Modifications Marauder Bullpup.
« Reply #7 on: July 14, 2013, 11:12:19 AM »
Thank you Mintie.. This little project has got soooo much international attention, I get multiple emails daily from people all over the globe wanting to buy one or wanting advice to help to make their own..
I is a very nice compact pcp and loads of fun to hunt with..

Shooting the 27.8gr Prems at 950fps MV gives me 26ftlbs at 100m, 18ftlbs @ 150 and still doesn't drop to 12ftlbs till about 215 meters so usable range is far in excess of the 100m mark..

I will fit up the scope cam and shoot a group at 200 meters on the next windless day for ya all..


  • Guest
Re: Modifications Marauder Bullpup.
« Reply #8 on: July 14, 2013, 11:13:45 AM »
Gets me about 13 consistent shots and 20 usable shots.. which is plenty for a hunting pcp :)

I have a 30cal barrel all machined up for it but haven't had a chance to fit it up test it as yet, still in the honeymoon period with my Russian bride ;)