I have personally experienced "Cold welding" of the bullet to the neck of a case.
Squeaky-clean brass, Jacketed bullet, and sitting for about 9 months as loaded.
The cartridge was 38-55 Winchester. The first 2 rounds fired showed no indications up
of any problem, but the 3rd shot was well out of the group, and when I extracted
the case, a good portion of the neck was missing, leaving a short, ragged-edged
case. I checked the bore. all seemed good, so I fired several more. At about #8, I got
another of the "missing neck" incidents.
Having enough of this nonsense, I packed up and went home. Took the remaining
12 rounds, and started breaking them down. Three of the remaining loaded rounds
were so welded, that I could not pull them with a collet puller.
I put these in my press [Bonanza CO-AX] and tried seating them a bit deeper so I could
pull them. One of the 3 broke free, the other two folded the cases just below the bullet base.
I had to peel the brass off the bullet with sidecutters and the metallurgical bond was
clearly evident, transferring copper to the brass case, and brass to copper as well.
I concluded that this phenomenon requires 3 factors to occur:
1. The case and bullet must be very clean.
2. The metals must be dissimilar or compatible alloys.
3. Some time must pass for the welding to take place.
No more super-clean cases for me!! I have ammo around that is 2 or 3 years old. I do
not want to experience this again. I now tumble dry exclusively, using walnut or treated
corncob. I can forego the shiny, shiny brass in favor of consistency and safety. Fortunately,
no apparent damage to my Reproduction M94 rifle. Dave.