why not take the sideline stab off and see if the gun fires with the co2 left in your tank? Is the tank aluminum or Chrom molly? I know I was always fooled into thinking I had more co2 in my chrome molly tank than my aluminum...

I know there are people out there that use co2 and leval 10 without only having 2-3 oz of usable air. I also dispute the leval 10 needing 850-900 psi to work right, I mean, my 800 psi output crossfire tank worked great on it, I still got shots off when it went below 800 psi, the gun continued to fire (even though the velocity was crap) until there was around 400 psi in the tank before it gave up...

Just my thoughts...