ScopesAndAmmo.com Store Logo

+ Reply to Thread
Page 1 of 2 12 LastLast
Results 1 to 10 of 11

Thread: What O-rings to get for QB78 valve and gas tube end cap?

  1. #1
    Member Dukemeister's Avatar
    Join Date
    Sat Dec 31 2011
    Location
    Kingston, Ontario
    Posts
    177

    What O-rings to get for QB78 valve and gas tube end cap?

    I tried a Buna-N 70D O-ring for the gas tube end cap - it worked for a single charge, but the socker swelled up 25% - it's obviously not a suitable material. Now, I knew this from the get go, but I was surprised at how quickly it swelled and by how much.
    Anyhow, just looking to find out what is the right size and material for these 2 O-rings that come in contact with the CO2. I used -113 size and that seems to fit well.
    I've seen some recommend Viton and some Silicone? Can Viton serve for both or Silicone for both?
    Member, Limestone Beekeepers Guild
    Duke ))))----//----------==

  2. #2
    Member Dukemeister's Avatar
    Join Date
    Sat Dec 31 2011
    Location
    Kingston, Ontario
    Posts
    177
    I posted same questions on UK Chinese Forum, response was to use EPDM. And, -113 is the correct size.
    The Buna N seal did shrink back to nominal size over the next few hours.
    Related topic..
    I have been tuning and shooting a new-to-me QB78D. To test seals and function and accuracy I am shooting with 1 live CO2 cartridge installed first and one empty. Seals are good. As received, it was weak at 250 fps, so I didn't do an accuracy test, instead I went straight for a polish and debur. Speed is now up to the limit, but accuracy is less than my other QB78 family rifles which typically do ragged hole at worst at 10 yards. This one is within a quater, but definitely not ragged hole.
    Some questions:
    1. I have typically shot my other QBs rested and either bulk filled or tethered, and get ragged hole.s This is the first time I've attempted target shooting on cartridge and only one cartridge at that. Anyhow, I'm getting about 30 shots, but I haven't chronied each one. When I did chrony the gun before and after tunes, I shot 3 in fairly rapid succession and noticed a ES of less than 5 fps. So, with may one cartridge set-up, is it likely that target shooting 20-30s between shots would affect accuracy?

    2. Scouring the Yellow shows Archer believes the single most useful accuracy enhancer to be a muzzle brake (weight) for the 78. My 79 .177 shoots ragged holes at 10 yd and it has no brake/weight. So, has anyone noticed an improvement in accuracy with a muzzle weight on a QB78?

    3. I did a brass screw/compound re-work of the crown. Under a 10x loupe it looks smooth and even. No noticable improvement in groups (well maybe marginal). I do notice that pellets are stiff to seat in the breach. Wheras the bolt closed somooth as silk without a pellet, the last 1mm of travel has significant resistance with pellet loaded (some worse than others). I think the shirts maybe being damaged. Is there a remedy for this?

    Of course I am going to do some more tests (tethered, examine pellet condition, and try a brake), and will report on my findings, but would appreciate hearing your experiences.

    Thanks,
    Member, Limestone Beekeepers Guild
    Duke ))))----//----------==

  3. #3
    Moderator rsterne's Avatar
    Join Date
    Wed Dec 7 2011
    Location
    Coalmont, BC
    Posts
    1,266
    Pull the barrel and have a look at the chamber and leade.... If you point the barrel at a bright light and look into the breech with a 10X loupe you should probably be able to see if there is a burr.... Possibly when they drilled the transfer port it left a burr sticking up in the barrel.... If that is the case, careful work with a needle file will likely rectify the situation....

    Bob
    Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
    Airsonal: Too many to count!

  4. #4
    Member Dukemeister's Avatar
    Join Date
    Sat Dec 31 2011
    Location
    Kingston, Ontario
    Posts
    177
    Aye, thanks Bob I will try that next. I vaguely remember doing that to my AR2078... but it was a year ago and my memory is short.
    Member, Limestone Beekeepers Guild
    Duke ))))----//----------==

  5. #5
    Administrator AirGunEric's Avatar
    Join Date
    Sat Dec 3 2011
    Location
    Somewhere Out There
    Posts
    1,295
    Quote Originally Posted by Dukemeister View Post
    ...believes the single most useful accuracy enhancer to be a muzzle brake (weight) for the 78. My 79 .177 shoots ragged holes at 10 yd and it has no brake/weight. So, has anyone noticed an improvement in accuracy with a muzzle weight on a QB78?
    I would suggest that some sellers will suggest the "best" whatever is whatever they can sell (telling someone to re-crown their barrel isn't likely a big money-maker). While I have no specific response to this statement, I find it doubtful a brake is going to be the "single most useful" anything other than a cosmetic improvement. The QB is not all that lightweight nor all that powerful if unmodified (i.e. HPA)- so I think you're on the right track with barrel recrowning.
    I'd say I care- but I'd probably be lying...


  6. #6
    Senior Member sholo's Avatar
    Join Date
    Sun Jan 1 2012
    Location
    Slightly north of "out there"
    Posts
    354
    Quote Originally Posted by AirGunEric View Post
    ...I find it doubtful a brake is going to be the "single most useful" anything other than a cosmetic improvement, so I think you're on the right track with barrel recrowning.
    I would tend to agree, too.

    When I first got my AR, accuracy was less than stellar - quite bad actually, but after recrowning (removing nick at muzzle), widening the loading tray (was off-center, kept ripping bolt o-ring off), it is now a dream to shoot! With H&N Finale Match at 10 yards, I can pretty much put the whole tin into 1 small, ragged hole (benchrested, of course). For FT, I use JSB Heavies (10.34 gr) and when I practice on my range at home, can now consistently hit all spinners out to 55 yards (when there is no wind). I like my "new" factory barrel so much that I'm now having second thoughts on whether or not I actually need a LW barrel!

    As for using a brake, I found no difference at all in POI with or without. Having said that though, I AM using the factory one, but more just to hide the notches in barrel, plus I have it mounted about 1/8" past muzzle to protect the crown a bit. Maybe a heavier brake would yield different results?

    Todd
    Todd

    Don't sweat the petty things, and don't pet the sweatty things!

  7. #7
    Member Dukemeister's Avatar
    Join Date
    Sat Dec 31 2011
    Location
    Kingston, Ontario
    Posts
    177
    Well, Myth Busters says.... "BUSTED".
    But there is a cosmetic improvement .
    Tethered to 800psi HPA didn't help either.
    Breach and TP hole/burr it is... when I get the time. I did push a couple different pellets through the barrel, still mounted, and the softer ones (JBB RS and Daisy) had visible shear deformation on the heads (skirts were slightly knackerd, but it took considerable effort to get pellet moving with ultra thick weed wacker line).
    Attached Images Attached Images
    Member, Limestone Beekeepers Guild
    Duke ))))----//----------==

  8. #8
    Senior Member sholo's Avatar
    Join Date
    Sun Jan 1 2012
    Location
    Slightly north of "out there"
    Posts
    354
    Gun looks good, Duke!

    Brake looks to be same size as factory, only brass? I can see why your bottle is tethered, and not mounted... (could almost use that sucker as a benchrest!) Must get a phenomenal amount of shots...

    Quote Originally Posted by Dukemeister View Post
    ...it took considerable effort to get pellet moving with ultra thick weed wacker line).
    Isn't that kinda like "trying to push a rope"? ... (j/k)

    Todd
    Todd

    Don't sweat the petty things, and don't pet the sweatty things!

  9. #9
    Member Dukemeister's Avatar
    Join Date
    Sat Dec 31 2011
    Location
    Kingston, Ontario
    Posts
    177
    Quote Originally Posted by sholo View Post
    Gun looks good, Duke!

    Brake looks to be same size as factory, only brass? I can see why your bottle is tethered, and not mounted... (could almost use that sucker as a benchrest!) Must get a phenomenal amount of shots...


    Isn't that kinda like "trying to push a rope"? ... (j/k)

    Todd
    Hi,

    Well good news, I did some serious polishing of the leade and burr at TP inside the barrel. There was a big burr as expected, and the transition lip was very sharp. It took much careful filing, sanding and polishing. I must have worked on it for 4+ hrs. Anyhow, the result now is 10 pellets touching at 10m (indoor range on HPA) - with JSB Exact RS - the softest pellets I have. Perhaps with the right pellet it'll do single or ragged hole - but the result is very promising.
    My shooting buddy at work asked me why I have 3 of the same rifle. Well, they are just so much fun to tweak and turn into shooters. Besides, each one is quite different!
    What to get next? Sure hope Umarex does bring us the XS60C...

    BTW, the brake I made out of scrap brass pipe, 15.8 mm ID 3/4" OD, and shimmed with photo film to fit on the barrel. It was my first project on the lathe, not professional quality but it's my own doing and is functional. The HPA tank has given me roughly 2 shots per pump stroke, and that's 400 shots between 3000 psi and 1200 psi with my AE2078 .22 which hasn't been tuned for efficiency (on the to do learning curve for a future project.) The tethered bottle make the rifle basically a bench rest necessity, one reason I'm doing up my 79 with a 90g CO2 bottle.
    Member, Limestone Beekeepers Guild
    Duke ))))----//----------==

  10. #10
    Member Dukemeister's Avatar
    Join Date
    Sat Dec 31 2011
    Location
    Kingston, Ontario
    Posts
    177
    Quote Originally Posted by Dukemeister View Post
    The HPA tank has given me roughly 2 shots per pump stroke.
    Wishful thinking? No, just writing too fast. I get 2 shots for 3 pump strokes...
    Member, Limestone Beekeepers Guild
    Duke ))))----//----------==

+ Reply to Thread

Similar Threads

  1. 22xx tube bleed hole and Disco valve
    By sholo in forum Co2 and Pre-Charged Pneumatic (PCP) guns.
    Replies: 27
    Last Post: Sep 30 2012, 05:04 AM
  2. Replies: 1
    Last Post: Aug 03 2012, 06:02 PM
  3. WTT AR 2078 air tube with key for QB 78 trigger
    By paddyfritz in forum For Sale
    Replies: 5
    Last Post: Jul 20 2012, 12:04 PM
  4. 3000 psi tube QB78
    By remtom1200 in forum Co2 and Pre-Charged Pneumatic (PCP) guns.
    Replies: 64
    Last Post: Feb 17 2012, 04:01 AM
  5. Wanted Leupold/Millet Low rings-22 cal pellets
    By FootedShaft in forum Wanted/Where to Find in Canada
    Replies: 7
    Last Post: Jan 19 2012, 03:49 PM

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts