I had always considered most .30-06 ammo to be pretty stable, but chemical reactions seem to continuously pop up where you least expect them. These cartridges with the stannic Model 1906 (pre-M2) bullets have apparently been corroding for some time while stored in zip lock bags in their stripper clips. The primers appear to be the sole source of the corrosion as pulling the bullets revealed the powder and the insides of the cases to be unaffected. The headstamp is F A 37, from lot 1982.
I noticed some deterioration on some FA 41 and RA 42 .30-06 today although these were in a batch of odds and ends which may have been contaminated by some older stuff. Common rounds, so it was easy to just trash these. We may be nearing the end of the shelf life of the huge stocks of WW2 .30-06 ammo which have kept shooters happy for many decades.
This was one of the reasons, although by far not the most important, that I stopped collecting the 7.9 x 57 mm cartridge. I would look at a German steel-case round on Monday and it was mint. On Wednesday, it was covered with plums of rust that had broken thru from the inside. I pulled bullets and cleaned out the powder, sometimes noting that part of the base of the bullets were eaten away already. With one round, the top half of the cartridge-case went with the bullet when an attempt was made to pull the bullet with an inertia bullet puller. That was happening more and more. The example cited (Monday/Wednesday) was allegorical of course, but not far from the truth.
A shame. I could not come up with anyway to stop these rounds from self-destructing. I have had primer leakage hurt specimens in several different case materials, but it has been minor so far compared to the problem with German (and from German occupied countries) steel-case cartridges. So far, none in 9 mm, but perhaps it is because of a different type of powder that doesn’t case this severe internal rusting.
I’ve always found 8mm Lebel to be the worst offender. I’ve stopped actively collecting the caliber due to its deterioration.