Cayugad has a lot of good advice in his post. Personally, I leave mine loaded all season and, if no opportunities come along for a harvest,keep it outdoors. Never have had a problem. Somewhere I read that pellets are more resistent to moisture issues than loose powder. One thing I have seen, though, is that it can be very difficult to seat a sabot when the temps are on the low side. I once tried to seat a Barnes 250 Expander MZ in a T/C Black Diamond when it was 7 degrees above zero. Would not go down the barrel. Couldn't get it to go back out, after removing the breech plub, either. Took it back to myshop and left it for three hours in room temperature - came out without much trouble. These rounds seat pretty firmly in summer temps, but in cold weather you couldn't seat one with a hammer.