Hi.

Anybody used one of Johns "1250 PSI 13Cu In" bottles on a QB97? I'm concerned that 1250 psi may be a bit high for safety. Would this pressure be sufficient to drive a 0.177 8.8 grain pellet at 800 or so FPS?

Do Johns regs have blow out disks on the low pressure output side?


Regards Ora

The burst disc on a C02 tank goes off at 1800 psi and is considered safe so a HPA bottle filled to 1250 psi should be no problem even if it doesn't have a bust disc. HPA doesn't expand like C02 under hot conditions.

Since stock QBs stop going up in MV and start going down about 90 degrees (lower pressure about 1050 PSI) my guess is that's what happen with air unless you rework the valve and hammer some.

I'm betting the MV will be less than with 850 PSI.

Doug Owen

I would strongly advise against using a pressure as high as 1250psi with a standard main tube. As Doug indicates, it's some way above the maximum pressure of CO2 at the valve lock-up temperature. You might get lucky, but I certainly wouldn't do it myself!

In the past, I've talked to the factory in detail about the design, materials and manufacturing specifications for the main tube and have always received somewhat evasive answers about any potential use BEYOND that for which the tube was designed. This tells me that while the specs are perfectly satisfactory for normal use with CO2 - as we all know - there is no certainty of safe operation if higher pressures are used. This is why I always advise against any increase in pressure with these guns unless a high quality replacement main tube specified for a higher pressure is used - such as the Jack Haley conversions.

Stephen Archer
Archer Airguns Inc.
http://www.archerairguns.com

presumably one is for the low pressure side.I'd buy one set at 850,and mod the valve to get the power I wanted.Don't you have to work under a 12 ft/lb limit?

I have a RFM tuned QB79 (.177) as well. I am shooting Crosman premier HP's( 7.9g) at 890 f/s on 1000 psi HPA. My tank and reg are from Mat Bean and I purchased them at the 1000 PSI pressure specifically for the QB79. I was shooting kodiak match pellets at 10.6g and 825 f/s on Thursday giving me a super consistant 16 ftlb gun.

I couldn't be happier !

Thanks,

Jay

I have one of John's tanks and it does have the blow out disk for the output side and the other for the full tank pressure.
I have a qb79 with a 1200psi tank from Matt Bean and it shoots a lot slower than a qb78 supplied with the same psi via remote.It doesn't have valve lock though because when you shoot it below 1200 it just gets slower.It shoots just over 700fps,the qb78 does that on co2 and 850 fps with hpa at 1200psi.It's a .22 cal with 14.5 gn superdomes.

Is your rifle tuned ?
My other qb79 22cal tuned by mike melick shoots 750 f/s crosman
fpointeds 14.3g off 1000 psi HPA tank on the gun.

Jay

It has a tapered valve stem,Some extra holes drilled around the puncture pin.It has a 1/16" probe at 1 3/8 inch length,and barrel porting.I had the spring shimmed some but I didn't like the effect on the trigger so I changed that.It has the icemaker tube seal replacement. I expected 780fps or better with hpa but 735 is the best I've seen.My umarex 850 and also my qb78 will break 700fps with co2 so I'm disappointed with this one but it is a very accurate gun.

Have you tried it at 1000 psi ?

My setup sounds similar but the back of my valve has been opened up and the valve spring may have a coil clipped. My hammer spring is stock as well. I see little change in going from gun mounted tank to remote

Jay

on a 79 you won't see much,if any difference between gun mounted or remote fed,but a long body tube will very likely yield a good size gain.That seems to be the common experience.
Some way of gun mounting a reg'd bottle while still using a long tube would likely be the ultimate..but how to do it and not be too ugly?

I'm working on a valve with a conical spring against the valve stem and maybe cut off 1/2" or more off the aluminum end of the valve. I got some of this idea from this forum a while back.This will give me a little larger air capacity in front of the valve .I've used this same valve and barrel on a qb78 and it was a 100fps faster so it must be the area in front of the valve making the difference.