Wonder if you can help with this one fellas?

My E9A (which as far as I can tell, is remarkably similar to the EB20, though it is actually called 'Crossman Model E9A Series, Cartridge Valve), which has not seen much use, is firing with a very varied muzzle energy.

Mostly sitting just under four, but then doing a few crazies at eight to ten. Is it possible that, as it's not been used for some time (if even used at all), it simply needs running in?

Pellets are .20 Field Target Trophy (15.1 grain?). CO2's are Crossman, installed with a little moly around the nozzle.

Wondering if to, and how to polish the internals. What would I polish? Seems very straight forward to dismantle.

Can anyone tell me the difference (if there is one) between the E9A and the EB20 please? Does this term 'cartridge valve' have any significance?

Cheers.
PESCA