Firing split brass? What would happen?

[Unclenick]

The government and private cartridge manufacturers started annealing bottleneck case necks and shoulders after the mechanism of season cracking was worked out and reported in 1921, but I don't know exactly how long the adoption took to become universal. As a result, I would expect anything made in the 1920s or earlier might possibly suffer from it, though military ammo was fast to adopt the practice.

I've had bad surplus ammo with the aging powder problem. The corrosion not only ate through cases (verdigris around the edges of the hole) but also corrode the bullets into fusion with the case, so there would be a hole at the bullet location in the case, but the bullet couldn't be pulled without stretching the case or tearing it open.

Never shoot loads with powder that is going bad like that. I put quite a number of those rounds through an M1A, and the nitric acid radicals caused fine bore rust to coat the "cleaned" bore. I then used Iosso Bore Cleaner, which is a mild abrasive like JB Bore compound, to be sure of removing the affected iron atoms, but since nitric acid fumes are used to intentionally create fine surface rust in the traditional steam cabinet rust bluing process, I suppose I could have pulled the barrel and boiled it in water for ten or fifteen minutes to convert it to black magnetite and then brushed the loose particles out. Evaporust might have worked well, too, but this was about 1994, and I don't think that product existed then.

The other reason never to shoot deteriorating powder, even if your barrel is stainless, is sometimes the deterioration can occur in a fashion that preferentially deteriorates the powder's deterrents. When that happens, the powder's burn rate goes way up, so you are shooting at higher pressures than normal. There have been photos online of rifles burst by ammo from the 1940s that was suffering from that problem, including a couple of Garand actions, which are extremely strong. So bad powder is nothing to fool with. It has to be disposed of.