Metal plate stopping a 19th century bullet?

Your question makes perfect sense. You want to know the penetration of a particular bullet at a specific speed into a specific metal.
We do a lot of shooting in this neck of the woods. (I figured you Texans would, too)
A high speed 22 from a rifle 1200 fps will go through 7 inches of pine. It will pass through 1/8 aluminum like butter.
My 38 special will pass right through a car door and out the other side if I use non expanding ball ammo with a jacket and a +P cartridge.
A .44 Magnum will penetrate an engine block and seize the engine if you hit it near a cylinder
The penetration also depends upon the angle you hit the object. If I hit an 1/8 steel plate at 45 degrees with my .38 it will barely leave a mark. If I hit it straight on I will dent it so far the steel will split. The .44 will pass right through.
Figure an AR-15 .223s or AK-47 will go through anything less than 3/8 inch think.
There are too many variables and combinations, none of which am I willing to try on my person.

Thanks @worriedguy . Would this be applicable to guns made in the mid to late 1800s?

I’m pretty sure that Marty was shot by a lever-action rifle, correct? Or perhaps a revolver.

Either way, the gun probably fired what would likely be the .45 Long Colt round, which averages about 1000 feet per second in velocity and disperses about 480 foot pounds of force.

That’s somewhat slow compared to modern centerfire rifle rounds, but it is still capable of penetrating a piece of iron, depending on the thickness of the iron.

Like today, bullets were made of lead back then so the results would be similar. We have higher power, faster burning powders but there is a physical limit to how much stress the gun can take. Also remember for every action there is an equal an opposite reaction. There is a limit to how much punishment your hand or shoulder can take. Sure, the military can use armor piercing bullets made of depleted uranium but for us regular folk lead is it.
My son has a particular revolver that I shot once and found it so painful I never did it again. My shot completely exploded a 1 gallon jug filled with water. Awesome power.

I’m pretty sure that those old stoves were cast iron and has a tendency to shatter when hit by a point impact. It isn’t very thick metal. Ammo back in the day was round on its front or more blunt. not like the pointed spitzer boat tail projectiles of .30 caliber-ish in modern weapons. The old ammo was also larger in caliber like .45, and .50 which carried a lot of kinetic energy like a speeding wrecking ball. There’s no surprise there were so many amputations in the US Civil War because of that size ammo. Those old guns were nasty.

So, in essence, it would be a bad idea for me to drape cast iron plates around my body and expect to not get hurt by a Colt .45?

@mrentropy, technically, what is colloquially referred to as a Colt .45 (in actuality, the Colt 1911) fires a .45 ACP round, which is different from the .45 Long Colt that was likely represented in the film. (The .45 ACP is more modern)

I wouldn’t do it. Even if the round fails to penetrate the force of impact is still bound to knock the piss out of you. In which case you might fall down and hit your head against something and get maimed in some way.

I think it would probably stop the slug. Ned Kelly got into a fire fight with the police wearing cast iron armour and the reports from the time suggest it was very effective. (Although if I remember correctly he didn’t have any armour on his legs which in retrospect was probably an error).

@Lightlyseared, yes, he was also shot with black powder rifles which have significantly less velocity than centerfire rifles, though.