I agree that the hole in the photo looks kinda small. Also, seem to recall that reversing the plenum tubes is how you can switch to FAC vs sub12. Not easy to do! Can’t find this on YouTube, though…..
Just an fyi- If you use a urethane o-ring of the same hardness-90 durometer, it should last a bit longer(wear-wise and chemical resistance-wise) than butyl rubber(nbr).
Looks like the normal pellet port. It is the one normally used for pellets. If there isn’t a slug port on the other side( guessing this is a single port) then the only way to get mor power is to make that hole bigger. What caliber?
I had an issue with the sear scoring the hammer(not the hammer weight!). I was getting wild swings like yours. I spoke with a tech at Utah AG and he advised that this scoring made irregular releases of the hammer and weight. Look closely at the area where the sear touches the hammer. This issue...
If you want an easy way to tune, check out Shooting with Phil on YouTube. His stuff really works. If not, there are MANY videos on how to tune. I, also, have a .22 Maverick Compact. Terrific, accurate gun! Great choice for a first pcp!!