Strange velocity bulk fill QB78

[Jonah]

Shooting my QB78 today on bulk fill of .9 ounces (25 gram) fill and velocity was only running 370 fps to 400 fps when it should have been about 564fps.. Degassed gun and installed only one full 12 gram CO2 cartridge and one empty cartridge and velocity was at 564 fps. Can’t see anything to cause the lower velocity on the bulk fill.



Anybody have a brilliant idea as to what is happening? The gun has always shot well on bulk fill. Would not be valve lock on CO2.

 

[Chuck-in-Ohio]

Sounds like you filled with gaseous CO2 instead of liquid.



New tank? If so, check that it is a siphon tank, and invert it if it is not.



Second guess is that the rifle was still chilled from the fill, and velocity stayed low as a result.

 

[Jonah]

Tank is a 20 ounce CO2 tank and it was inverted.

 

[Chuck-in-Ohio]

Did you have your C02 tank filled at a store, or fill it yourself?

The worker drones in stores are well known for bodging up the fill if they don't know the procedure, resulting in you getting a partial fill or worse.

 

[Jonah]

I fill my 20 ounce tanks from my five pound tanks. Been doing that for several years. Five pound tanks are inverted when filling the 20 ounce tank.