We have just finished pulling the bullets on one lot, quantity 118, of .30-06 M2 ball ammunition made at the Twin Cities Army Ammunition Plant in 1943. These rounds belong to a friend and, to his horror, he discovered recently quite by accident that virtually all of them had corroded primers. He bought these rounds still in the USGI 5-round stripper clips and bandoleers at the AGCA Birmingham gun show some years back, put them up in an M19A1 "thirty-cal" can with some desiccant packs and forgot about them. He owns a US M1917 Enfield so the 5-round strippers were perfect for him.
Now the can has been stored in the proverbial cool, dry place so my friend was at a loss to explain how moisture had got into the can. The stripper clips on some of the rounds were corroded as well, yet the can's integrity seemed to be intact. Did he pack them away on a humid day without verifying that the desiccant packs were fresh and activated? He doesn't recall. It could be simply the fact that the ammo is corrosive primed and 70 years old. In any case, We're going to reload the pulled bullets into the same cases after a good tumbling.
One problem we've run into is that because the cases have never been fired, the primers are still locked tightly in the primer pocket. The tremendous pressures generated in firing actually loosens the primer within the case, as well as stretches the brass, and this makes it easier to punch out. What is happening with a good percentage of the cases is that the decapping pin is actually punching a hole through the primer rather than dislodging it from the case. I will let you know if we manage to salvage these cases.
In any case, it is a cautionary tale for those of us who have put back ammo. Take the time to carefully inspect your stocks (once a year is not a bad idea), Put in fresh desiccant as you go. Don't end up betting your life on corroded ammunition.