Author Topic: QB/AR & HPA custom project = many questions  (Read 3372 times)

Offline DougT

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QB/AR & HPA custom project = many questions
« on: January 20, 2010, 03:59:18 PM »
I've got a .22 high-powered springer that I've been shooting for 1.5 years and really like it but I want to add a gas gun to my gunsafe.  After MANY, MANY hours on this forum as well as others, I think I've come up with a plan.  The QB or AR seems to be the best start, as it seems the equivalent of the small block Chevy: cheap, reliable, easy to work on and parts are easy to find.  This would be a .22 used for some informal target shooting and hunting at 20-75 yards.   I have a home machine shop at my disposal.  I am not a" pro" machinist but do have considerable creativity, visiion and determination.   Here are my goals for the end result.

1.  Be very accurate.  1" groups at 50 yards would be acceptable.  Consistant velocity seems to factor in here, especially when shooting past 50 yards, which I do a lot.
2.  Have good power.  A 14.3g pellet at 850fps+ is the goal.
3.  Have a long shot count.  At LEAST 100 full power shots before refilling.  Preferrably 200 or more shots would be desireable.
4.  Be reliable.
5.  Reasonable cost (not have to sell a kidney to finance the project).
6.  Be reasonably easy to work on and get replacement/upgrade parts.
7.  Look similar to goodgroup's modified QB         http://www.gatewaytoairguns.com/airguns/forums/thread-view.asp?tid=16652&mid=135173#M135173


Before I commit and start purchasing, there are some  questions I have.  If anyone knows the answer(s), please chime in.

1.  What are the differences between the QB and AR series rifles?  I understand that the QB78 & QB79 are the same rifle except for how the CO2 is provided.  It looks like the AR2078 is a restocked QB78 with fancy sights and an AR2079 is a restocked QB79 with fancy sights.

2.  Is any one of these a more accurate rifle in general?  Do the AR rifles have a better barrel?

3.  How hard is the gas block to remove?  I'll be converting this gun to HPA and probably run a 47 cu.in. tank with a 1100# regulator on it so it will require a custom "dropped" gas block.  The 47" tank is 3" in diameter so a 5/8" drop should work.  The 13 & 22cu.in. tanks are about 2" in diameter.

4.  Has anyone used the JRA? multi-shot breech with the rotary magazines?  

5.  Can the gas tube be shortened?  I'm wanting to get the larger air cylinder as back as far as possible.  I'm thinking of cutting the tube shorter, leaving just enough length ahead of the front of the valve to mount the drop-gas-block.

6.  If you run 1100# HPA in this valve, will I have to do work on the valve or replace parts to achieve the desired power?  I see that goodgroup runs a RFM valve and gets the power I'm looking for.  Is this necessary?

7.  I haven't seem much on power adjusters.  Can one be fabricated for this gun?

8.  How good (or bad) is the stock trigger?  I'm thinking of reworking the trigger with custom parts.  

9.  Is the safety a pain to use?  It looks like you have to rotate the safety lever to engage/disengage the safety.  I'm thinking of a lever type in front of the trigger like my TF-89.

10.  How difficult is loading this rifle with a scope on it?  I'm wanting to use a Leapers Bug Buster 3-9X32 scope.  Will a compact one-piece mount work or will it need to be 2-piece mounts?

11.  I plan to use an AR2078 stock and modify it to accept the air tank and lengthen the LOP.

12.  Is there anything I'm overlooking?

Thanks to "ribbonstone" and "goodgroup" for sharing their custom guns.  

Thanks for any info.
Doug



Hammerli 850 HPA .22 & Leapers 3-9x32  --  TF-89 .22 & Leapers 4x32
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2010 air rifle kills
288 starlings
235 pigeons
6 crows
25 other birds
56 ground squirrels
3 tree squirrels

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2009 air rifle kills
181 various birds
57 various squirrels

Offline ribbonstone

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RE: QB/AR & HPA custom project = many questions
« Reply #1 on: January 21, 2010, 02:13:31 PM »
Will answer what I can...hopefully others will cover the parts I'm unsure of.

Goals:
Think all of those goals can be met...the 1" at 50yards is going to be very dependent of the luck of the barrel draw, finding the pellet the gun likes best, and the shooter.  100 shots per fill?  No problem at all if you do decide to use that 47CI tank (1100psi).

Questions:
#1/2:  The AR's ae considered a bit more accurate.  I'm not 100% sold on that, but that does seem to be the majority view.  You'll want the bigger stock for modification into something like the posted picture anyway. Might save a few $ by buying used as you're going to cut on it anyway.

#3.  gas block is easy to remove...two screws and it pulls right off.  Haven't a clue ho you'll get to make a drop-down large enough to use a tank that fat, and wonder just how well a gun with that large a tank would handle.  I really suspect that a 47Ci tank would make it look like a tank wearing a gun rather than a gun wearing a tank.

#4. Prefer single shots, so have no opinion on that (other than JRA is a nice breech, and the larger foot-print to the gas tube is probably an accuracy help).

#5. The QB79 length tube (or the AR tanker version...same tube) is about as short as you'd care to go.  Not much room between tank-block and valve on those tubes.  Thee needs to be air at least some "on deck" (between the regulator and the valve) for best results when trying for this level of power.  

#6. To get to 850fps, you'll need to do a bit of valve fiddling.  Would replace the valve stem with a Delrin version, but the issue one will work for at least a short while.  With HPA, have to think in terms of how long the valve stays open.  Can't up the pressure, so faster speeds require a longer push of 1100PSI air, and to get that longer push the valve has to stay open longer....so you'll have some valve/hammer/spring tension fiddling to do (you can get that speed, but the gun is going to use a good volume of air and be a bit n the loud side).

#7. Not real easy.  Have been some posts on converting to a cock-on-closing action, which would be needed in order to externally adjust the striker spring.  Could convert to a two-operation...bolt just loads, a seperate cocking lever added (by milling) to the gas tube...either way, it's not a simple conversion.

#8. Trigger can be adjusted.  Can replace the trigger pins, shim out the slack, and a little touch smoothing here and there get it to a more than decent pull.  

#9. Safety is a pain.  That 180 degree rotation sucks; no som much for getting the safety from on to off (which you can do with a strong flick of your trigger finger), but nearly impossible to get from off to on without dismount from your shoulder.  Either ignor it, remove it, or modify it (have a 90degree rotation mod that I've posted in the past, and if you get to that point in your build, will post it again).

#10.  Two piece. Short scopes kind of suck as they tend to put the fat objective over the loading port; full length scopes work out better. It's not a problem to load for me, and if it is for you, get high mounts.  My philosophy is that if you're going to jack the scope up, may as well make use of it being up there and get a scope with a large objective lens.
Robert

Offline tjk

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Re: QB/AR & HPA custom project = many questions
« Reply #2 on: January 23, 2010, 12:22:43 AM »
Wow!!! Now that's alot of info!!!! Thanks RS! Getting ready to jump off the fence and get a QB model,...yet I have much to learn! tjk
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