Not many gun owners here are there? Or if so, none that were ‘brave’ enough (or stupid enough) to find out about bullets firing without benefit of a chamber.
Most will explode harmlessly if dropped into a fire, but I can pull the head off of a .22 with my fingers. Especially from cartridges which are cheaply made. Those will fire out of the brass. As a kid with more guts than brains, when camping, I did a few ‘experiments’ and hid behind a sand hill. Bullets dropped into a fire will shoot the round out rather often in odd directions.
See, most cartridges, after discharge, will drop out of the cylinder of a pistol. That indicates they did not expand much at all. Some do, which is why most revolvers have an ejector mechanism. A brass tube, with a slug loosely plugged in the end will act like a cannon with a ball dropped in it. The better the quality of the round, the firmer the fit of the slug, complete with some crimping of the brass lip into the lead. That gives a split second for the powder charge to build up more power before forcing the slug out. Those shells would probably explode.
Now, brass designed to be salvaged a reloaded is different because it is thicker. The rim, or opening of the cartridge is often not crimped but the slightly oversized slug force fitted into it. Especially reloads. Repeated crimping of the brass would damage the cartridge.
Plus, many high powered shells are formed like a two stage missile. Bigger in the base then smaller where the bullet is. The large base could allow pressure to build up and the extended neck let the slug blow out before the case ruptures.
Rimfire cartridges can easily be fired by hand, with pliers and something to strike it with. (Done it.) Especially if you grip the cartridge in the middle with the serrated jaws of the plier. A shotgun shell can be fired by striking the detonator cap in the center of the base while holding the brass part with something. The recoil there is savage though and you’d have to be standing within inches of your target to hit it.
Many shotgun shells are plastic, but made to be reloaded a few times. You can open the crimped shot chamber easily with the tip of a pocket knife. Many people who do a lot of shooting find it cheaper to buy reloads which are not sealed as tightly as the new rounds would be.
I don’t suggest experimentation. Especially with shotgun shells. I was lucky.
There is also the possibility that hundreds of brass rounds, stacked in ammo cases, one on top of the other, could, by weight alone and density, act like a restricting firing chamber and allow some slugs to fire off without blowing the casing apart.
I don’t figure Koresh always bought top of the line munitions.