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Author Topic: My QB79 .25 - "The QuarterBore79"  (Read 44994 times)

Offline Raizer

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My QB79 .25 - "The QuarterBore79"
« on: April 02, 2013, 12:38:08 AM »
Not really sure if its worth starting a thread on this gun, but I'm bored and can't sleep so might as well!

Some of you guys might remember me getting a Mike Melick power tuned .22 QB79 back in August last year, I had a thread on the old boards where I was rather excited about its arrival haha





Then I added a DIY silencer



And when I was really lucky I would get groups like this

But only with JSB pellets

And most of the time they were more like this  :-[

If not much worse!

Did take a few possums with it but only managed to hit maybe 1/2 the birds I tried to shoot  >:(

With advice from Wingman and others I went through many possible causes of the problem, from bad crown to clipping in the silencer (which it was but drilling it out didn't help the problem).

In the end it turned out that the bore in the barrel was larger than it should be and the pellets weren't engaging the rifling much if at all, I could push a 5.50mm pellet (tin stamped 5.53) through using thin weedeater line and very minimal pressure

The marking looks a lot deeper in the photos than in person!
Also the probe/bolt seal and transfer port seal were both leaking a bit.

So I got talking to Wingman a while back about going to .25, since I had been lusting over his B-Rod in all its BSA barreled glory  :P
And now I've got a .25 choked BSA blank on its way from the UK!

I've started prepping the gun for its transformation this weekend by opening up the front of the valve as much as I can, getting the port in the valve to align with the hole in the tube and figuring out a higher flow option for the transfer port while ditching the orings the stock barrel was floated in.

So yeah thats about where it's up to  :)



« Last Edit: July 22, 2013, 02:43:22 PM by Raizer »

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Re: My QB79, soon to be .25
« Reply #1 on: April 04, 2013, 09:48:53 AM »
This is definitely a subject worthy of a thread, I'm sure other proud owners of the Qb model c02 and hpa air guns will be watching to see your results.



Offline Raizer

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Re: My QB79, soon to be .25
« Reply #2 on: April 09, 2013, 03:42:54 PM »
Customs Declaration
1x rubber oring
1x grease
1x steel tube for machining

declared value: 15

 ;D

So my barrel arrived this arvo, haven't taken it out of the bag yet, but just looking through the plastic the blueing and rifling looks really nice!
Kinda disappointed it doesn't have the BSA logo stamped in it haha



(the "oring" is a new breech seal for my Hatsan)


Edit: as I said in the shout box the other day, an angle grinder and a power drill are not a good substitute for a mill or lathe!
My valve piercing body isn't looking too great  :-[


But I've got another one coming from the UK now and a much better idea on how to go about opening it up (the key is a longer valve spring!) so hopefully round 2 will end up a bit like this one!
« Last Edit: April 09, 2013, 07:21:55 PM by Raizer »

Offline Raizer

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Re: My QB79, soon to be .25
« Reply #3 on: April 11, 2013, 03:13:06 PM »
Take 2 went a lot smoother, one slip of the grinder though but it didn't make too much of a mess




I tried to find a longer valve spring, this one looks like it should fit but is a little bit softer?

Offline Wingman

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Re: My QB79, soon to be .25
« Reply #4 on: April 11, 2013, 10:58:25 PM »
Here's a quick progress report for ya.. I have turned up a new .25 cal bolt probe and turned the barrels breach down to a very snug polished fit which requires a soft face hammer to send home..



This will be a far better means of attachment than the factory undersized breach floating on those 3 soft O rings and one retaining grub screw allowing it to slop all over the show with the slightest knock. The new fit is so snug that it wont in fact require any O rings to seal it. I will put it in the mill tomorrow and open up the feed tray section of the breach.



I will turn the bolt probe down a bit thinner and shape the tip of the probe to fit the rear end of a JSB King perfectly aiding bore to pellet alignment further.
The Kings are a perfect candidate pellet for this project as they are light, short and tend to out shoot any other pellet in all .25 cal rifles. The challenge you now face is blasting enough CO2/air up its skirt to get them moving..
The bolt will have a tapered touch fit to a shoulder just inside the breach like a Theoben Rapid with an additional breach O ring just behind that.

I gave the bore a good scrub to rid it of the factory crud and have pushed a few pellets through the new 1/4" bore and there is plenty of bite in this bad boy.. the choke is nice and tight and the pellets exit showing good strong rifling grooves in the head and skirt.


Offline Raizer

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Re: My QB79, soon to be .25
« Reply #5 on: April 11, 2013, 11:17:16 PM »
Wow you work fast mate!
That is looking really great to me!!

Thinking that if you don't have a use for that match grade .22 barrel ( :P :P) I might try and split it to get a pic of just how nice the rifling was lol

I really can't thank you enough man!!

Offline Davey

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Re: My QB79, soon to be .25
« Reply #6 on: April 12, 2013, 06:42:18 AM »
I forget how the QB probes work, do they discharge air through an opening in the probe or past it? Your new one looks like flow-past but I thought I remembered some being flow-through... because if it is past, not through, then you probably want as skinny a probe as possible to allow for max flow. If it is through, then no prob, carry on.
 
Intrigued to hear how you get on.
The spreadsheet guy.

Offline Raizer

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Re: My QB79, soon to be .25
« Reply #7 on: April 12, 2013, 08:02:39 AM »
The factory bolt has a flow through the probe, but mine came with a Mike Melick custom probe with a drill bit glued in for a flow past pin.

Offline Wingman

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Re: My QB79, soon to be .25
« Reply #8 on: April 12, 2013, 09:05:00 PM »
We Raizer, Your Qb79 is officially a .25cal! The barrel is fitted and I have cut the sweetest JSB chamber in it sized perfectly for the Kings.
I also shaped the bolt probe tip to suit the internal skirt angle... tomorrow I will machine a groove in the bolt to add a breach O ring and a mod to the transfer port sealing surfaces to fit a decent O ring.





That will only leave the crown and 1/2x20tpi muzzle thread to complete before hopefully some testing on paper tomorrow..




« Last Edit: April 12, 2013, 09:21:36 PM by Wingman »

Offline Raizer

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Re: My QB79, soon to be .25
« Reply #9 on: April 12, 2013, 10:03:35 PM »
That looks AWESOME mate!!

Hopefully the other co2 bottle will be delivered in the morning, its not showing up on the tracking yet but they stung me $10 for Sat delivery so it should be there!

*I sent a freshly filled co2 bottle to Wingman with the gun, but it was over pressurized and the valve seal is jammed up in the pin valve so no gas will come out.

Offline Raizer

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Re: My QB79, soon to be .25
« Reply #10 on: April 14, 2013, 07:22:24 PM »
Just got a text from Wingman, he ran out of light for chrony'ing but "its smoking those Kings out"  ;D

Offline Wingman

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Re: My QB79, soon to be .25
« Reply #11 on: April 14, 2013, 08:27:39 PM »
Ive cut the breach seal groove and fitted an O ring.. Ive tested it under pressure and it shows no leaks at all..







I have reassembled the rifle and put a few shots through it but it got too dark to chrony.. judging by the hole in my fence it will be quite the possum slayer now.. Will do some velocity and group tests tomorrow and get it back to you. Its just screaming out for a Hpa conversion now..


Offline Raizer

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Re: My QB79, soon to be .25
« Reply #12 on: April 14, 2013, 08:33:46 PM »
 ;D ;D ;D I am seriously in awe of your machining skills mate! I can't wait to shoot it!!

Just have to ask though, did you end up putting a thread on the muzzle?
I don't want to be a pest, but I can't use it at home without a silencer  :-[


Offline Wingman

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Re: My QB79, soon to be .25
« Reply #13 on: April 14, 2013, 08:38:38 PM »
Not yet but will do it in the morning for ya along with the new bolt knob:)

Offline Raizer

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Re: My QB79, soon to be .25
« Reply #14 on: April 14, 2013, 08:41:46 PM »
Thanks mate!!  :D