Single, double, or safe?

No relation to baseball, promise!  Single, double, and safe are all types of actions on semiautomatic pistols.  The action refers to what happens when you pull the trigger.

 

Ammunition Anatomy

I really wanted to call this Anatomy of a Bullet, but that's technically incorrect, and I'll explain why below.

As I'm shooting, I tend to think of questions, rather than keeping my mind on what I'm doing.  Maybe that's why I keep missing? Anyway, I figure the best way to get these questions out of my head is to answer them.  Today, we are going to look at the anatomy of ammunition!  I'm specifically looking at centerfire rounds, though the principles are the same for rimfire and shotgun shells.

There are four basic parts to each round.



1) Casing

From Starline Brass

Cartridge cases are generally brass.They contain the powder and primer and hold the projectile in close proximity to these explosives.  The crimp is the part of the cases that crimps or curves inward to hold onto the projectile.  The head (closed end) of a casing seals the back of the chamber to force the gasses forward and expel the projectile.  The base of the casing has a rim that is gripped by the extractor to remove the empty casing or to prevent the round from moving to far into the chamber of a revolver.

2) Projectile

This is the bullet, and why I couldn't title this post anatomy of a bullet, as that would be over fairly quickly.  I'll have to get to ballistics eventually though!  Most bullets are made of lead and some have copper or other jackets. In general, bullets are designed to expand on impact.  There are frangible (breakable) and other types of specialty rounds for unique uses.

3) Powder
Powder is the general term for the compound that produce gasses to push the projectile out of the barrel.  Historically this was black powder, which is a combination of charcoal, sulfur and saltpeter.  Most modern powders are 'smokeless' compounds of nitrocellulose and/or nitroglycerin

4) Primer
This is the collective term for the chemical primer compound, cup and anvil which is located int he head of the case.   When the primer is struck, it ignites the priming compound.  The flame travels through the flash hole to ignite the powder. 




How does it all work together?

• The firing pin impacts the primer
• Ignition of the priming compound
• Flame moves through the flash hole of the casing
• Ignition of the powder
• Burning powder creates large amounts of gas that expand the case to seal the chamber 
• Gasses push the bullet down the barrel 

If you'd rather see this information in video form, check this one out.

Rimfire v. Centerfire

Terminology Lesson 2: Rimfire versus Centerfire

These terms refer to the way that the cartridge of the round.

In centerfire, the firing pin hits the primer, contained in a firing cap, in the center of the base of the catridge.  If you look at the casing after firing centerfire, you see a round divot in the center, as below.  Centerfire ammunition is the most common style for military and law enforcement.  Centerfire cases are made of thicker metal than rimfire, which allows them to withstand higher pressures, and thus can be fired at higher velocities.  In addition, most shotgun shells are centerfire, though they typically use a  plastic casing.  Centerfired casings can be reloaded (another topic for later, replacing the primer, gunpowder, and projectile.

From a 9mm Beretta 92FS

In rimfire, the firing pin strikes the rim of the cartridge base.  The rim acts as a percussion cap for the cartridge.  The firing pin leaves a notch type depression on the edge of the casing, as below.  Rimfire casings must be made out of very thin material to allow for the necessary deformation by the firing pin to ignite the primer.  This deformation means that the cartridge cannot be reloaded.  However, this thinner casing allows for rimfire ammunition to be much less expensive than centerfire.  Almost all modern rimfire guns are .22 caliber or smaller, though historically rimfire was used in firearms up to .44 caliber. 

From a .22 match rifle

Extra bit:
Semi-automatic vs. revolver ammunition.  Semi-automatic casings have an inset rim (but are generally referred to as rimless) that allows the extractor to remove the casing after firing.  Revolver rounds have a rim at the base to prevent the round from moving too far into the cylinder, which would prevent the firing pin from reaching the base and firing the round.  I'm on the hunt for a good picture of the difference, we don't have any revolvers in the house...



As always, I hope you learned something.  I know I did in writing this! What do you shoot?  Everything in our house is centerfire, but I got to play with a friend's .22 match rifles and scoped target pistol this weekend.  Tons of fun!

Do you have a terminology (or other) questions?  I'd love to write about anything y'all think is important.

Semi-automatics: How do they work?

Being me, I like knowing how things work when I'm going to be using them.  At least the basics that is.  To that end, I wondered how all the internal spring etc of a semi-automatic pistol work together to load the ammunition, eject the casing, and cock the hammer.  I found this you tube video. 

Please ignore the cheesy 1980s-ness of it  It does a great job of explaining the process, despite horrifying mustaches.

If you want even more detail, try this Glock video.  You'll have to read, but it does show every little part.