I knew this, but I didn’t KNOW this. It was only when I started to trod on the shottist’s path that I truly thought about this interesting, to me, topic. It’s a nooby epiphany, if a mild one.
When the firing pin touches off the primer cap on a cartridge, and that, in turn, ignites the propellant, then tremendous pressure build up. At first, the seated bullet holds that pressure in, then bursts free of the tip of the cartridge and then makes its merry way on down the barrel to freedom. Sweet freedom.
Well brass is a softish metal. The walls of the case are relatively thin, too. The brass deforms and expands to fill the space it sits in in the receiver. This space is a close fit (or should be) to the cartridge that goes in it, but it isn’t perfect. If it was perfect it would be hard to get a cartridge to actually go INTO the hole. So there is a bit of wiggle room. A very small bit. And that wiggle room would lead to gases sneaking back around the cartridge and back toward the shooters face, except that the expanding case makes for a tighter seal.
If you compare a cartridge case that has never been fired with one you just fired you should be able to see the difference in shape, and probably with the naked eye.
Because of this phenomena, reloaders have to reform the brass back into place to get the whole thing back into original spec.
Because of this phenomena, reloader have to be careful not to reload too often, lest the reformed metals get thinner and weaker over successive reloads.
Because of this phenomena, many recommend against reloading rounds that are intended for semi-automatic rifles. Or at least to be very choosy about the brass you use. Compared to a bolt action rifle, a semi-auto is VERY hard on the brass, jamming the cartridge home at full spring pressures, and, even MORE violently, ripping a hot fired piece of brass out of battery and ejecting it away at the speed of the gas pistons pushing that bolt back, minus the strength of the spring. Thin brass can fail on this eject and you only pull out the very bottom of the case, or everything below the case neck, but leaving a ring of the neck behind. Then in a blink of an eye the semi-auto tries to jam a fresh round up in there when there is still big bits of brass cartridge in there. This is a bad jam at minimum, and an abject disaster if it slam fires the round. Bad, bad.
Because of all this, if I reload the brass for my Garand, I will be SURE it is quality thick brass, and fired only once. Jeez that can be scary. And it would be my own damn fault if I had a cartridge failure. It a big argument for eye-protection. It makes me think about forehead protection, too.
Dumb idea, also won’t happen - So, some guy wants to get a bunch of gun guys to march on Washington. Only with their loaded rifles. I’m told he tries this every year and no one but a few...
37 minutes ago