You correct that regulator issue by “Purging” your rifle prior to hunting. ( take to shots into the ground then hunt.
The best airguns in the world need to be purged, ie; FX M4 . This should fix issue so you get consistent FPS
I highly suggest a quality rifle which you control its power. I highly recommend the FX tactical 30 cal without bottle. This will keep the gun light and you will get 23 shots out of a fill and shoots 45g pellets and STACKS THEM! (Puts one on top of the other).
This gun is of average price range...