QB-78 Bulk Fill Pressure Sanity Check

[Kallysan]

OK just doing a sanity check.  I was looking at classifieds and came across one for a QB-78 Carbine with a bulk fill adapter, the poster claims he has been filling to 2800 psi with HPA instead of CO2 for the last two years.  To me that is an INSANE and is a bomb waiting to go boom. Am I just misinformed?  It is a CO2 gun not a PCP.  Below is a link to the add.

http://www.airguns.net/classifieds/show_ad.php?adNum=106190&adSort=&StartingAd=0&NumberOfPages=6

[N6CRV]

OK just doing a sanity check.  I was looking at classifieds and came across one for a QB-78 Carbine with a bulk fill adapter, the poster claims he has been filling to 2800 psi with HPA instead of CO2 for the last two years.  To me that is an INSANE and is a bomb waiting to go boom. Am I just misinformed?  It is a CO2 gun not a PCP.  Below is a link to the add.

http://www.airguns.net/classifieds/show_ad.php?adNum=106190&adSort=&StartingAd=0&NumberOfPages=6

If you want it better get it FAST before Mark blows himself and the gun up. No it is NOT made to run those pressures. I guess you can be lucky but for how long is the question.

[Gerard]

As rsterne has often said on this subject, the tube may well be up to such high pressure but the retaining cap almost certainly is not. Staying under about 1,800psi is probably okay (pressure of CO2 on a hot day) but going to 2,800 could easily make a bullet out of that brass fill adapter. Not a safe gamble. I've got one of those adapters and have run as high as 1,800psi without problems. But only a couple of times. I'll feel safer when rrdstarr gets my dropped tank adapter finished and I can run about 1,000psi in the QB78's main tube from a regulated Ninja tank.

[rsterne]

The valve attachment is also in question at those pressures.... Some QBs actually have a space between the valve and the steel backer block, so that both the screws are not taking equal loads.... Using that much pressure on the fill cap retaining nut is really pushing it.... particularly if the O-ring on the fill plus is not back on the full tube thickness but on the threaded portion.... Just a whole lot of reasons not to do this sort of thing....

The problem is not so much doing it once, as doing in repeatledly.... Metal fatigue is a problem once the safety margin of steel parts is less than 2:1, and they are likely to eventually fail.... If you are running a QB on HPA, PLEASE USE A 1.8K BURST DISC.... or NEVER FILL BEYOND 1800 psi (which means don't ever let your hand slip)....

Bob

[Kallysan]

Bulk fill CO2 works just fine with me.

[lillysdad621]

I have the same setup. only fill to 1500 psi.mine holds forever and has been setup like that for now 4 years... 2800 makes me cringe.