"You need to release the tension on the firing pin during storage (once you get it repaired)."
Take the safety off and pull the trigger before you put it away.
http://www.cheaperthandirt.com/SNAP801-5.html
BTW - I don't use a snap cap in my autoloader, but I do in all my other shotguns.
No need to use them with centerfire rifles, but also should use them with rimfires (i use spent shell).
To be clear - You need to release the tension on the firing pin during storage (or not - up to you)