FX Impact Compact M3 Small Game Tuning

Just bought a Impact Mk3 Compact .22 in April

ATN 4K 4×14

Hand held thermal

Portable compressor

Moved up from a Beeman R1 .177

I want to focus mainly on rats, starlings and pigeons in barns at night.

Shooting Crosman 14.3 HP ($10.00/500 count)

20yrds max 

What FPS would you recomend for clean kills and higher shot count on my 300cc

Any suggestions on tuning/settings.

YouTube not very helpful on what I'm aiming for. Low Power Hunting.

Thanks USMC