the 177 penetrates deeper due to less frontal diameter and greater velocity. the 22 still has better killing power on animals larger than birds. i do ALL of my small game hunting with air guns. i assume you meant PBA ammo? if so, DO NOT use that stuff in your beeman. you will burn your seal and break your mainspring. it's too light and lets the piston slam into the front of the compression cylinder and any of the "supersonic" alloy pellets are a gimmick because velocity sells. usually never accurate, and even when it is, lead will be moreso. in 177 stay away from anything lighter than 7 grains and 22 nothing lighter than about 13grains. your gun will last longer and you will be more accurate.