Primers used to be made with a compound that left a corrosive salt residue in the firearm. U.S. made ammunition manufactured up to the mid 1950’s is suspect, as is foreign made ammo up to about 1980. It’s a problem, and if you’ve seen an older rifle that wasn’t properly cleaned, it will have a dark, pitted bore.
I have some of this ammo in 30.06, with headstamps from the ’40s and ’50s. It’s been sitting in an ammo can, isolated from the newer stuff and the reloads. But if you never plan to shoot it, why keep it around? So yesterday I took it to the range, along with my 1903A3 and sent about 30 rounds down range, as practice ammo for upcoming Garand matches.
I had planned to clean it right away when I got home, but then it was time for dinner, so I set the ’03 back in the safe next to the Garand.
Two hours later I came back. The 1903A3 had completely dissolved, leaving just the stock and sling and a pile of rust. The Garand next to it had pitted to the point that it will never be usable again. I took a picture of my folly:
Oops, sorry, got sidetracked by the gun forum warnings.
Actually, two hours later, I came back and got the ’03 and cleaned it. I had a couple of ideas, using ammonia and then hot water to remove the salts, then a regular cleaning, but decided to look around the interwebz to see what was recommended. I found this thread on the CMP forum and used what I learned there in addition to my own ideas to clean the rifle.
My baseline idea is that this was the only ammo available for decades and all these old rifles used it. The rifles survived it then and have come down to us in serviceable condition. Proper cleaning is possible, just time consuming.