QB tomfoolery...

QB tomfoolery...

Joined: March 16th, 2009, 1:43 am

April 12th, 2011, 2:24 pm #1

Yesterday I started to play with a bulk kit for the qb78 in .22 that i have been home tuning for a while now... It was shooting RWS hobbies at 550 fps and it would get about 45 shots with the powerlets... Now mind you i have redone the seals and the transfer port, and played with springs in search of power and bumped it about 45 fps from stock...
After putting it back together i flirted again with a PCP idea, filled it up to 1500 psi and started shooting... It gets 15 shots... about 10 of them at a consistent 640 fps with crosman premiers (14.3) and then it looses about 20 fps per shot... so i stop shooting it when it gets to about 520 fps... So as a PCP hunter it will do the job... it is just LOUD... I am leary of keep filling it pass that, as when i run calculations i came up with 1990 psi as a pressure failing point for the original tube. So i run it at 75% to be safer... I wonder how many shots that would yield...
Well after that stint i emptied it and then filled it from my CO2 tank and ran a string through the chrony... Bulk filled that rifle gives me 36 consistent shots averaging 580 fps with the RWS hobbies. It is also much quieter and puts out 9 FPE in a very accurate and civilized manner. I think i am goint to keep it like that... it will be a great yard gun at that powerlevel.
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Joined: August 3rd, 2007, 1:55 am

April 12th, 2011, 3:59 pm #2

Hi Gabe;

I was just wondering if you reinforced the valve in any way???
May Your Day Be Special
Ray
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Joined: March 16th, 2009, 1:43 am

April 12th, 2011, 4:11 pm #3

No sir. The valve had some port work, but due to the fact that it butts into a metal spacer that is held in place with the breech screw and the stock screw, it seems secure enough to hold pressure and valve in place.
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Joined: August 3rd, 2007, 1:55 am

April 12th, 2011, 4:28 pm #4


May Your Day Be Special
Ray
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Joined: August 3rd, 2007, 1:55 am

April 12th, 2011, 6:21 pm #5

Yesterday I started to play with a bulk kit for the qb78 in .22 that i have been home tuning for a while now... It was shooting RWS hobbies at 550 fps and it would get about 45 shots with the powerlets... Now mind you i have redone the seals and the transfer port, and played with springs in search of power and bumped it about 45 fps from stock...
After putting it back together i flirted again with a PCP idea, filled it up to 1500 psi and started shooting... It gets 15 shots... about 10 of them at a consistent 640 fps with crosman premiers (14.3) and then it looses about 20 fps per shot... so i stop shooting it when it gets to about 520 fps... So as a PCP hunter it will do the job... it is just LOUD... I am leary of keep filling it pass that, as when i run calculations i came up with 1990 psi as a pressure failing point for the original tube. So i run it at 75% to be safer... I wonder how many shots that would yield...
Well after that stint i emptied it and then filled it from my CO2 tank and ran a string through the chrony... Bulk filled that rifle gives me 36 consistent shots averaging 580 fps with the RWS hobbies. It is also much quieter and puts out 9 FPE in a very accurate and civilized manner. I think i am goint to keep it like that... it will be a great yard gun at that powerlevel.
Hi Gabe;

I was wondering if you might have tried preloading the hammer spring at all???
May Your Day Be Special
Ray
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Joined: November 17th, 2006, 3:51 am

April 13th, 2011, 12:54 am #6

No sir. The valve had some port work, but due to the fact that it butts into a metal spacer that is held in place with the breech screw and the stock screw, it seems secure enough to hold pressure and valve in place.
..valve isn't going to set back without that steel ring moving, and it's held in place by two beefy sized screws.

The issue outer ring of the bulk fill end cap is probably the weak spot, although the tubes have never seen a pressure test and are a wild card. I'm not really comfortable with the idea of filing the issue tube, not so much becasue of the tube, but becasue some of the end cap rings are not all that well threaded to the tube. While I haven't made one go "boom" (yet) even though i tried in experiments, suspect that is the weak spot.

10 resasonably consistent shots at that pressure is as good as you are likely to get.
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Joined: March 28th, 2002, 6:54 pm

April 13th, 2011, 4:44 am #7

Yesterday I started to play with a bulk kit for the qb78 in .22 that i have been home tuning for a while now... It was shooting RWS hobbies at 550 fps and it would get about 45 shots with the powerlets... Now mind you i have redone the seals and the transfer port, and played with springs in search of power and bumped it about 45 fps from stock...
After putting it back together i flirted again with a PCP idea, filled it up to 1500 psi and started shooting... It gets 15 shots... about 10 of them at a consistent 640 fps with crosman premiers (14.3) and then it looses about 20 fps per shot... so i stop shooting it when it gets to about 520 fps... So as a PCP hunter it will do the job... it is just LOUD... I am leary of keep filling it pass that, as when i run calculations i came up with 1990 psi as a pressure failing point for the original tube. So i run it at 75% to be safer... I wonder how many shots that would yield...
Well after that stint i emptied it and then filled it from my CO2 tank and ran a string through the chrony... Bulk filled that rifle gives me 36 consistent shots averaging 580 fps with the RWS hobbies. It is also much quieter and puts out 9 FPE in a very accurate and civilized manner. I think i am goint to keep it like that... it will be a great yard gun at that powerlevel.
and delrin head valve. Put a bored out or wire probe bolt above that, and expect to see 900 fps with those 14.3 pellets on 1100 psi air,low 800's on co2
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Joined: June 21st, 2009, 8:05 pm

April 13th, 2011, 11:13 am #8

Where can I get a valve such as you describe ?
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Joined: September 21st, 2007, 12:13 pm

April 13th, 2011, 1:50 pm #9

has these for sale from time to time.
You might try contacting him..
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Joined: January 24th, 2003, 3:54 pm

April 17th, 2011, 1:18 am #10

Where can I get a valve such as you describe ?
Sorry... I'm dumb. N/T
Last edited by Arved on May 6th, 2011, 6:46 pm, edited 1 time in total.
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