I shoot a lot of surplus military ammo, some of it as old as seventy years, and I always clean after each session. You can't trust the old stuff. I found out the hard way that com-block ammo that had been loaded as recently as 1996 was corrosive. Rusted the bore on my otherwise pristine New England Westinghouse Mosin Nagant .
On my 22s, I never clean the bore. It just doesn't seem to be necessary. The actions are a different story, especially the autoloaders.
I think an M3A1 grease gun just might give an AK a run for its money when it comes down to "get filthy and still function" test. I was 45 Bravo in Germany in 1969-70. Small arms repair. I spent months at a time at the ranges at Grafenwohr, with a tanker's M3A1 and all the ammo I wanted to shoot, when I wasn't trying to fix that miserable contraption known as an M-73.
I had four mags that actually worked and I must have put 10,000 rounds through that thing. Never cleaned it, never had a single stoppage. It had a paste- like residue everywhere inside the receiver (like a 22) but it never quit. At some point during all this, the hook on the extractor decided to go on R&R, and left the gun, apparently hitching a ride with a bullet. As it is a blowback operated mechanism, the gun ignored all of this and kept chugging along.
I discovered this when I tried to clear the gun in the middle of firing a mag. Since it seemed to still work, I kept right on using it. When I finally DID clean it, I saw the ugliest gouge in the barrel you will ever see, no doubt made by the bullet shoving the extractor out the front.
