I always fire to clear at the end of the night, im not comfortable leaving a charge in the barrel, primer or no primer. Some powders/pellets are more corrosive than others and I am somewhat a clean freak when it comes to any of my firearms. Thats just me, plus most mfgs reccomend clearing the barrel before any storage, overnight or through to the next season. Several places online sell those Co2 barrel clearing gizmos, never tried one but ive heard they are useful. Other option if you can is to unscrew the breech and let it drop.