QB78 HiPac conversion
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QB78 HiPac conversion
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Topic: QB78 HiPac conversion (Read 7105 times))
Ribbonstone
GTA Senior Contributor
Posts: 12030
QB78 HiPac conversion
«
on:
June 04, 2013, 12:51:23 AM »
QB 78 HiPac conversion tube arrived today (US Post). Will come in a shrink wrapped mailing tube.
<a href="
http://s157.photobucket.com/user/ribbonstone/media/HiPaC/e0fc8d5f-c3b5-4d7e-9405-41df5225950e.jpg.html
" target="_blank"><img src="
http://i157.photobucket.com/albums/t50/ribbonstone/HiPaC/e0fc8d5f-c3b5-4d7e-9405-41df5225950e.jpg
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Basically, a conversion tube and a black seal.
<a href="
http://s157.photobucket.com/user/ribbonstone/media/HiPaC/eb8afe02-c37f-42ee-9db2-c96da240c822.jpg.html
" target="_blank"><img src="
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" border="0" alt=" photo eb8afe02-c37f-42ee-9db2-c96da240c822.jpg"/>[/url]
Well machined and blued unit. Can tell it will be low volume, so shot count won’t be very long.
So how do you convert a QB 78 (or the AR2078)?
1. Pick a test gun. This one is a nicely stocked, but was selected becasu eit was a coose to stock as I own.
<a href="
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" border="0" alt=" photo 4fccff34-ad56-4610-8d5f-d137fd190bf0.jpg"/>[/url]
2. Only things done to it are to remove the fiber filter in the valve. STOCK valve (with piercing pin) and restrictive transfer port. Transfer port is ugly, but it doesn’t leak (pretty don’t count).
<a href="
http://s157.photobucket.com/user/ribbonstone/media/HiPaC/604ca8de-ab9e-4509-a652-bd748993df56.jpg.html
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http://i157.photobucket.com/albums/t50/ribbonstone/HiPaC/604ca8de-ab9e-4509-a652-bd748993df56.jpg
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3. Disassemble until you have the valve in your hand (NOT going to do a take down guide. If you don’t know how to take down a QB, really should not EVEN CONSIDER converting to HiPac until you do).
<a href="
http://s157.photobucket.com/user/ribbonstone/media/HiPaC/c46d4491-a964-4396-a7c8-444b986a3989.jpg.html
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http://i157.photobucket.com/albums/t50/ribbonstone/HiPaC/c46d4491-a964-4396-a7c8-444b986a3989.jpg
" border="0" alt=" photo c46d4491-a964-4396-a7c8-444b986a3989.jpg"/>[/url]
PROBLEM: This old valve cracked that white o-ring between valve halves. Been in service for about 4 years, so it was due to crack. Replaced it with a new one and proceeded onward.
4. What we are after is the front part of the valve unit (the Al. section). The black seal is going to fit into that recess (a little silicon grease would be good).
<a href="
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" target="_blank"><img src="
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5. Once you have that black seal in place, put the gun back together.
<a href="
http://s157.photobucket.com/user/ribbonstone/media/HiPaC/68202e5d-09f3-4b41-8d4e-f5e8483f711a.jpg.html
" target="_blank"><img src="
http://i157.photobucket.com/albums/t50/ribbonstone/HiPaC/68202e5d-09f3-4b41-8d4e-f5e8483f711a.jpg
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6. HiPAc unti slides in like a great big long 12gr., Tighten HAND TIGHT (can be a good firm tighten, but still hand tight). Being used to QB end caps, you’d think the knurled section would be a free spinning part; IT IS NOT. Is made one-piece, just has the knurling for a grip.
<a href="
http://s157.photobucket.com/user/ribbonstone/media/HiPaC/057103f5-212e-4b60-90a1-886c57dea1e4.jpg.html
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http://i157.photobucket.com/albums/t50/ribbonstone/HiPaC/057103f5-212e-4b60-90a1-886c57dea1e4.jpg
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7. May as well fill it and test for leaks. Filled this one to 1700psi and listened for any leak (in a dead quiet house). Would be best to let it sit over night and see if the pressure drops (as some leaks are too slow to actually hear). Step it up to 2K and check again. Then 2.5K.
PROBLEM: had a little auditory leak at 2.5K. Leak seemed to stop by 2K. Tightening the conversion unit 1/6th turn (compressing it to that black seal) seemed to stop the leak at 2.5K.
8. Completed conversion (took about 20 min., but I was taking time to snap photos).
<a href="
http://s157.photobucket.com/user/ribbonstone/media/HiPaC/06c8288f-ed7c-4244-beae-3e33ad98d0fd.jpg.html
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http://i157.photobucket.com/albums/t50/ribbonstone/HiPaC/06c8288f-ed7c-4244-beae-3e33ad98d0fd.jpg
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<a href="
http://s157.photobucket.com/user/ribbonstone/media/HiPaC/cfdd0761-251c-4556-af80-fe589f61acd2.jpg.html
" target="_blank"><img src="
http://i157.photobucket.com/albums/t50/ribbonstone/HiPaC/cfdd0761-251c-4556-af80-fe589f61acd2.jpg
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VALVE FIXATION:
The valve rests hard against a large steel ring. That steel ring takes the forward breech screw in from the top and the stock bolt in from the bottom, which seems like a pretty solid valve fixation. There is also a small valve location screw.
If this proves to be less secure than it seems, will add more fixation (so far the valve has held still in the tube up to 2,900PSI in tests).
Beginning tuning: I will be working on this over the next weeks.
SAME valve, SAME transfer port that was giving 640fps with 8.4gr. pellets (7.6 foot pounds) on co2.
#1. BOX STOCK valve and the standard spring that works fine with co2 seems to peak at 1500-1600psi. Pressure higher than that results in lower speeds, becoming valve locked at about 1900psi.
8.4gr. @ 752fps ( 10.5 fpe), but only for 7-8 usefully close shots. Pretty lame, could do the same by just pump filling a standard QB tube to 1600-1700psi.
#2. Increasing just the striker spring got it running well at 2000psi. Velocity increased to 825ps with 8.4g. at 761fps with 13.4gr. (call it 127foot pounds). BUT I still only got 7-8 close velocity shots.
#3. Max effort. Put in enough spring to get it running well at 2900psi. Got 852fps with 13.4gr. pellets, for 21 foot pounds, but again only 7 or so shots in a useful range of velocity.
CO2 VALVES ARE AIR HOGS! CO2 uses a lot of volume, so the valves are made to move a lot of gas. Using those valves with air tends to move (and waste) a good bit MORE air per shot than co2.
Seems like it’s the dwell. Valve is just knocked open longer than optimal for air (but probably good for co2).
ONE (SIMPLE) SOLUTION:
Limiting valve opening/dwell. Are several complicated ways 9and I will get around to investigating them), but the BStanley O-Ring mod is simpler (and seems to work just as well)>
Reset the gun to run right at about 2100psi (which is just before the cocking effort starts to get stiff). Added a single o-ring (metric, listed as #113 in the kit) ahead of the striker, right up against the steel ring that retains the valve. Fits tight enough inside the tube it won’t move around and sits right up against that steel ring around the valve stem.
Can just see the o-ring peeking out at the front of the slot:
<a href="
http://s157.photobucket.com/user/ribbonstone/media/066ed28e-ef80-45d4-860b-070008bfc420.jpg.html
" target="_blank"><img src="
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Results: 750fps average with 13.4gr. (16.7 foot pounds) but am getting 15 shots in a good velocity range.
THINGS TO DO:
This is a box stock valve, still with the piercing pin, and un modded. Am sure there is a lot of speed to be gained with a dedicated PCP valve (no piercing pin, ported, delrin valve seal, etc). Will eventually substitute a modded valve.
Fiddle with o-ring thickness, which would increase or decrease valve dwell.
«
Last Edit: June 04, 2013, 01:08:14 AM by Ribbonstone
»
Logged
Louisiana
darren
Expert
Posts: 1154
Check the torque on the nut behind the but.
Re: QB78 HiPac conversion
«
Reply #1 on:
June 04, 2013, 01:09:20 AM »
Ribbbinstone,
Could you, would you....
Bulk fill that hipac with co2 and let us know how it dose vs the 2 12 gram carts?
Thanks for the help.
Darren
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lodi california
Ribbonstone
GTA Senior Contributor
Posts: 12030
Re: QB78 HiPac conversion
«
Reply #2 on:
June 04, 2013, 08:00:11 AM »
Don't think there all that much volume than the standard tube....maybe 20-25% (will have to do some internal measurements). The conversion unit is thickwalled and slides into the air tube.
Logged
Louisiana
darren
Expert
Posts: 1154
Check the torque on the nut behind the but.
Re: QB78 HiPac conversion
«
Reply #3 on:
June 04, 2013, 09:17:50 AM »
Thinking of getting one of these units with one extension and using it on a 2400kt .177
All stock except foe hi flow valve with pin still in place so carts are still an option
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lodi california
Ribbonstone
GTA Senior Contributor
Posts: 12030
Re: QB78 HiPac conversion
«
Reply #4 on:
June 04, 2013, 08:17:37 PM »
Always find room for another QB. Like the tankers, but there is a PCP in this mix as well (the 4th one from the left was the donor for the HiPac experiments).
<a href="
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Left to right:
.25 QB PCP
.177AR2078 HPA
5mm QB 78 HPA
.177 QB 78 carbine (co2 in the picture/HiPac now)
.22 QB79 HPA
.22 QB78 HPA
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Louisiana
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QB78 HiPac conversion