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Author Topic: Improving the accuracy from a Crosman 1077  (Read 2018 times)

Offline Mintie

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Improving the accuracy from a Crosman 1077
« on: October 18, 2017, 05:37:56 PM »
Hi Guys,

I didn't really take pics while I was doing all this work im afraid, and I wasn't the one to come up with most of these ideas either - I just googled "1077 mods" for a while wanting to improve what is to be honest a really crappy rifle from the factory.

To start I will explain myself. I bought a 1077 a few years ago, I shot a couple of hundred pellets through it and gave up without opening it up. It wouldn't group (like A4 sized at 25y), the velocity was unbelievably inconsistent and the trigger pull was horrific. So I got rid of it and forgot about them for a while. When the Benjamin Wildfire came out I thought it looked familiar and started watching videos about it and the 1077 again which stirred a bit of interest again. A cheap deal came up second hand so I grabbed it hoping maybe this one would be better than the last. Nope. Even at 7m the grouping was about 40mm and the velocity went from 480 fps to 351 fps over 6 shots (not super rapid fire but faster than a single shot loaded rifle). I guess I already knew this would be the case as I wasn't really surprised, so I got on with stripping it down for a closer look at why!

Somewhere during the years of manufacture Crosman made a few small changes to this model. The later ones often don't have all the screws holding the two halves of the receiver together, is missing an oring on a part referred to as the "magazine detent" and I believe there are some other small changes as I have seen some bulk fill kits as advertised to only suit some variants. The one I picked up was the later model.

The mods I performed and where I heard about them:

Detent oring replacement - Apparently helps to make the rifle more efficient and adds a few FPS. Fairly easy to do and these instructions are good, how much difference it made I don't know as I did a few other bits while I was at it. https://www.youtube.com/watch?v=oBhYc3NQXeE

Valve gauze removal - This was done while I had the receiver open for the detent mod. Very simple mod and just helps the Co2 to flow a little easier which helps keep it a little bit more consistent when shooting rapidly. All you need to do is separate the tube from the plastic receiver, remove the brass valve and unscrew the face that holds the seal in place, remove the seal and the gauze screen and then reverse these steps.

Added hammer weight - I read that this can help increase power a little so while the receiver was open I glued a bit of extra lead weight to the hammer to help it hit the valve a little harder, hard to know if it helped and I didn't weight how much extra I added sorry.

Trigger spring weight reduction - I managed to find a spring that was the right outside diameter and was a much lighter weight than the stock spring, this did help the trigger pull a bit but to be fair its still pretty bad. Worth noting that there is also a spring on the magazine that you are working against when pulling the trigger, I will replace that at some point.

Barrel stabilization - As part of the design there are two tabs at the receiver end that help to push the inner barrel forward to allow you to clear any pellet jams, this means the "inner" barrel on this rifle flops around inside a false "outer" and has nothing really putting any tension on it or even keeping it in one place vs the scope rail etc. The recommended fix for this is pretty simple really, knock the front sight off and push some thin foam down inside between the outer and inner barrels to stop it from floating around and then push the front sight back on. From all the mods I did I think this probably increased the accuracy the most.

Barrel outer bedding - This one is a little harder to explain but you will see what I am talking about when you have it all apart. The way the outer barrel is held to the large plastic molding (spacer between the stock and the barrel), the receiver and the bottom tube is pretty poor and it tends to wobble around quite a bit. I fixed this by "bedding" it with a hot glue gun which I feel has given the rifle a much more solid and stable feeling in the hand, before this it really used to wobble around a bit and all felt loose. Between this and the above inner barrel stabilization the rifle is now shooting good groups that clover 3 shots into around 8mm ctc.

I haven't really done these with the aim to increase power, more just to actually get it shooting the way it should have out of the box. It is shooting a bit hotter than standard now with the Geco Diablos shooting at 610-630 fps for around 6fpe but the main thing is that it is grouping well now and is much more consistent.

Future mods? Im not sure if I will bother taking this any further but if I did find the time it would probably get a wooden stock, a bulk full kit (maybe hpa?) and a Carbon fiber shroud.

Some before and after grouping pics, and a couple of the rifle.
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Offline Akzle

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Re: Improving the accuracy from a Crosman 1077
« Reply #1 on: November 11, 2017, 08:52:08 AM »
Nice job man.
if these are the ones i'm thinking of they share the double action from crosmans 357.
co2 benefits from long barrels and expansion chambers, you can open and mod the valve for increased volume which will give higher velo's and potentially give accuracy at longer ranges.

Offline Mintie

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Re: Improving the accuracy from a Crosman 1077
« Reply #2 on: March 11, 2019, 12:01:46 PM »
Small update on this as there have been people asking about 1077s recently on social media.

Since writing this thread I have tuned up another 3 of these and always seem to find the same results as above, well below average grouping and poor velocity consistency out of the box. The mods mentioned above always seem to pull the accuracy into line and give a slight boost to the power however so if you are sitting on the fence about one and want to have a tinker I would suggest you give it a go, once they rre sorted they are good fun for plinking at tin cans, very back yard friendly with a nice little carbon fiber suppressor on it too!

The groups pictured here were both full mags at about 18m
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Offline Pauly5

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Re: Improving the accuracy from a Crosman 1077
« Reply #3 on: March 11, 2019, 11:02:33 PM »
What calibre is that cotton bud?
HW98
HW97k
Tx200
S510
HFT500
Bobcat
Matador R2.5
HW40 (copy)
Daisy 953
P-Rod
1377
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Offline Dvlnme

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Re: Improving the accuracy from a Crosman 1077
« Reply #4 on: March 12, 2019, 08:22:45 AM »
had several these to over years bought them just as fun plinking guns but ended uo being very disappointed in them just same as you did and for the same reasons,had wondered if the pcp versions were any good,its great to see they can be sorted out and the accuracy really improved by few simple modds,and velocitys made not only more consistant but incresed significatly too,as they are lot fun back yard plinkers for very little money and extra box mags cheap as for fast reloads etc,conversion kits available for 88gr cylanders and refillable 88gr cylanders suitable for them available cheap enuf too,like mintie i have lot time for good co2 guns,as long as i can bulk fill them to keep costs down to managable levels,there lot shots in a 5kg co2 fire extingisher and bulk fill stations readly available from paint ball suppliers that easy to fit to co2 extingishers,think from memory i calculated bout 16000 shots in 5kg extingisher,with the sort accuracy mintie getting they be good for pest birds etc inside buildings Paul same as i use my old gamo g1200 rifle i bulk filled for mate.triggers can be improved a little by replacing trigger spring and mag springs,but facts are the triggers are just very bassic double action type revolver triggers,but can be set up to give a very predicable two stage type revolver trigger thats a significant improvement over factory trigger just by replacing these two springs but not much else that can be done due to all the plastic parts involved etc,i cut a cone on the rear the barrel to give a lead into barrel this prevented many of the jams i got from pellets not allways entering the barrel straight particually with flat nosed pellets,i found domed pellets were best in these guns for that reason.excellent post mintie.
 cheers mike

Offline Akzle

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Re: Improving the accuracy from a Crosman 1077
« Reply #5 on: March 12, 2019, 08:24:40 AM »
A leupold optic on a crosman, well beggar me i never thought I'd see the day!

Again, good shit. Cheers for the write up.

Will I be finding any of these turn up at Ron's?

Offline Novagun

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Re: Improving the accuracy from a Crosman 1077
« Reply #6 on: March 12, 2019, 10:11:26 AM »
I still haven't ventured into CO2. Might one day. I looked at the pictures of the 1077 and then at the price at Rons. $198.00.  Not with my money. The rat catcher maybe but then you have to spend more for the bits to make it good.
I have a Crosman 1400 in bits. It failed to pump and I took it to pieces and then lost interest. Maybe that could be converted. If  I got enthusiastic about it.
CO2 guns seem to me to be too expensive for what you get. The Gamo and Umarex offerings. Not for me.

Offline Dvlnme

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Re: Improving the accuracy from a Crosman 1077
« Reply #7 on: March 12, 2019, 01:42:48 PM »
co2 definately expenisive if relying on disposble co2 sources,particully if you want to shoot a lot,unfortunately co2 repeating guns are so much fun to shoot,you soon get thru a lot of disposable co2 cylanders which soon becomes rather expensive,the down side of co2 is that if you got no co2 then the gun is useless eh!!thats why the few co2 guns i have have all been converted to some form of bulk fill co2 that i then use 5kg co2 fire extingishers to fill,as get these extingishers full and for free,so have no co2 costs and more co2 than i will ever use.Unlike some i dont generally modify co2 guns to increase power levels as i have plenty pcp guns if i need power etc,i can certainly see why some preferr springers when it comes to costs etc and do appreciatly that a springer will allways work and requires no out side power source,but in my situation i never run out of co2 or hpa to fill my guns so this isnt an issuse to me.
tuning a springer is just as much fun as doing the same for a co2 gun,as its all about results and the enjoyment we all get from doing so and in the end thats all that really matters eh!!
 cheers mike