How interchangeable is ammunition?

This comes up now and again, and I haven’t posted a firearm entry for some time, so here’s a new one.

There are several calibers that sound like they should be interchangeable, but the truth is, there are slight differences that can lead to disaster for your fictional characters, and your real life ones.

Making Jacketed Bullets

In another section I went over how to make cast lead bullets. There is a limit to how fast these can go. That’s one of the reasons for jacketed bullets.

A modern bullet is normally two parts. There is a lead core to give it the mass and a copper jacket to hold it together before, and after, it hits. There are other types, but the copper jacket represents the bulk of the market. While far less common than casting lead bullets, there are people who make their own jacketed bullets.

Making Bullets (cast)

In another section we went over how to load your own ammunition. This one is different. This is how to make your own bullets. From (nearly) scratch.

First up is cast bullets. These are far more commonly found made at home than jacketed ones. As with making most things, you need equipment. In this case, you need moulds, a furnace, a sizing press, and lube.

The first thing to keep in mind is that:

Reloading

It probably goes without saying that no company actually makes silver bullets or rounds filled with holy water or garlic powder for those pesky vermin that come sniffing around some stories. Fortunately, it’s really not all that hard for a person to make their own conventional ammunition. This is not completely without risk, but it’s possible. Specialty stuff is a little harder.

How easy is it?

Exterior Ballistics, or Bullets in Flight

Exterior ballistics is just a sciencey sounding word that is used to describe anything flying through the air.  Could be bullets; could be snow balls.

This is a very math intensive area, but I’m going to do my very best to keep the math out of it as much as possible.

Once a bullet leaves the barrel of a gun, or a ball leaves the hand that threw it, it is at the mercy of physics.  Where it goes is determined from the moment it breaks contact, unless the wind messes with it.

Look at a baseball.  When an outfielder throws the ball to second base, he doesn’t throw it at the second baseman.  It would never get there.  Instead, he throws it up, in the direction of the second baseman.  Air resistance slows the speed of the ball and gravity pulls it back down.  The same thing happens to bullets.

Bullets

One of the things I’ve seen the most in writer’s forums is confusion about the type of gun vs. the type of round.  I’d like to hit that part first.

A 9mm Parabellum has no idea whether it’s begin fired from a Glock, a single shot Contender, or an MP5 submachine gun.  When people ask for a powerful handgun, someone almost always brings up a Glock, but never mentions the caliber.  This is a danger sign.  Don’t listen to these people.

There is no real difference in power between the Desert Eagle in .44 magnum and the Smith and Wesson revolver Dirty Harry used to teach basic math in 1971.  If they have the same powder charge and the same bullet, they will have basically the same effects.

So, what does “caliber” mean?

Parts and Names of Parts

Before we can get into the different types of guns and how they work, we need a list of common terms.

A fully loaded Cartridge consists of four things.  The Bullet is the part that flies out of the front and does the damage.  The Powder is what burns to make that happen.  The Primer starts the powder burning, and the Shell or Casing holds it all together.

Shell casings come in two basic types and two basic configurations.  Handguns tend to use straight wall cases.  This means they are about the same diameter at the top as they are at the bottom.  Rifles tend to use a bottle shape where the neck of the case is just big enough to hold the bullet, while the bottom of the case is much larger.  This allows them to hold more powder, and increases the power of the round.

The other two differences relate to the Rim of the case.  The rim can either stick out slightly, like a small, stubby L, or it can be recessed in so the diameter of the rim is the same as the diameter of the case.  This is the best indicator of whether or not the case was intended for use in a vertically stacked magazine, as used in most modern semi automatic actions for both rifles and pistols.  Recessed rims are called Rimless cases.

Collectively, all of this is called a cartridge, or Round.  It is also sometimes called a bullet, though that is technically the name for just the bit that flies out.  The Bullet can also be called a Slug, though that is an outdated term unless dealing with a shotgun that fires a single projectile.