Now you guys are string the pot!!I'm not going to try and convince someone that aluminum or Steel cases didn't destroy their gun. I just don't understand the mechanism behind this theory that all aluminum or steel is bad. How many rounds of these other than brass cases does it take to destroy one's gun? One, two, ten, hundreds, thousands?
I am quite certain there are lots of firearms that failed after one round of brass cased ammunition. As you have more or less pointed out, the case is a gas seal, call it a gasket. If the gasket fails, high pressure gas escapes. It can cause part erosion, or, it can increase the load on the firearm and break it. Such as burst receivers.
In terms of reliability, brass is the "Gold" standard. Cartridge brass is well characterized, well understood, had been the optimal material for almost two centuries now, give or take. Brass has the best material properties to date and a well made brass case turns out to be a very reliable thing.
Other materials have their risks. I know the Germans used steel cases in WW1. They were running out of copper and tin, so they experimented with steel. These steel cases worked, but the Germans had to coat the cases in a wax lube or the steel would stick in the chamber. The Germans made and shot billions of these lubricated steel case 8 mm Mauser rounds, but they never expected to re use them.
No one who makes steel or aluminum cases recommends them for more than one use. I am going to say that is because the material properties change after multiple uses, material flaws propagate, and the risk of failure increases to an unacceptable amount.
In so far as new aluminum cases, reload and shoot them. They manufacturer of the things was confident enough of the things to use them in new ammunition, the risk of using new aluminum cases is probably on the same level as new brass cases:an acceptable risk. However, I would never use aluminum cases twice because I am not risk tolerant. I have used up so many of my chances that the next accident may get me.
