Hello, so I am completely baffled by this. I have an FX Impact X 600mm 0.22 cal barrel shooting 23gr NSA slugs with a power plenum installed. When I first installed the power plenum, when the regulator was set at 120bar it was shooting at about 940fps with the hammer spring preload set correctly, the hammer spring set to max and the valve stem adjustment all of the way out. Last night I was running a test and with everything else the same it was shooting 920fps. Then at the end of my test (over 100 shots later and about 3 hours) it was shooting 905fps. The velocity drop happened after I took the bottle off and bled the regulator to turn the screw in to readjust the reg back to 120bar. I thought maybe the gun for some reason gets all messed up every time you bleed the reg, so I did it 3 times today and it had no effect on muzzle velocity. I tried to see if maybe the chronograph’s velocity readings “walk” over hours of use, so after over 24 hours of being off I turned it back on. Same muzzle velocity. Now today it is shooting 890-905 fps. I cleaned the barrel and that didn’t help. The reg gauge isn’t showing any reg creep so that isn’t the problem. I lubed the slugs more and less and neither helped. And yes, I made sure the tank pressure was far away from the reg pressure to minimize any problems with variations in gauge readings between the two gauges. Also, all of these tests were done in my basement, with the lights off (this is a light chrono so I use the lights that come with if.) so we can rule out light variations or the chronograph not being level because of wind pushing it. What is going on?!?! Could the gun be dirty inside and need to be cleaned? Maybe the valve stem is getting dirty? Please help. I’ve run every test I could think of to pinpoint the problem and have failed to find an answer.
