Storing any ammo in "potentially" damp environments can be problematic. Steel cases, such as commonly used in surplus 7.62x39, can rust. I had 5 bricks of Winchester Super X .22 ammo laying on the floor in the basement. Sump pump quit working and got an 1" of water in that area before I got a new pump installed. Got the 7.62 ammo dried out OK, but I thought the .22 would be OK. Turns out whatever coating Winchester puts on the .22's turns really waxy when exposed to dampness. Even the ones that weren't immersed, but the boxes got damp from the water wicking up. Now the .22's won't feed after about a box of 50 are run through my Ruger 1022. The rotary magazines gum up and won't feed. This is a major nuisance. They work better in my son's bolt action, but they still get harder to extract after enough are shot. I'll probably have to pitch the two rotary magazines after I am done with the ammo. I don't think they can be taken apart and they don't seem to clean out all the way. I am finally down to my last brick. I won't be buying anymore Winchester .22's.

Keep your ammo dry and look closely at any ammo you are storing for long term use.