Caliber 101...

I've been asked by someone who shall remain nameless to give a primer of sorts (ha! a gun pun!) on the various and sundry calibers available to the new shooter. Said person is looking to enter the world of the gunnie, and is understandably overwhelmed by the sheer volume of calibers and information - both good and bad - about the various and sundry options. I figured this would be a three part series, starting with pistol calibers today, rifle calibers tomorrow, and shotgun gauge on Thursday.

There is simply no way to cover - even as a skim - all the various permutations out there. Shooting Times has an excellent ballistic table for many rifle and handgun calibers which covers the velocity and the energy of the round both at the muzzle and out to 50 yards. Different bullet weights and types are covered in this table, which can be used as a rough comparison of one caliber to another.

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For starters, let's run through some of the acronyms the new shooter is likely to come across:

ACP: Automatic Colt Pistol. Refers to a round designed by John Moses Browning (PBUH) for use in autoloading firearms. All ACP-designated rounds have the same proportional dimensions.
FMJ: Full Metal Jacket. Refers to a solid-tipped bullet, usually copper.
LR: Long Rifle. Designation for the most common rimfire round of them all.
JHP: Jacketed Hollow Point. Refers to a bullet with a hollow center designed to "mushroom" upon hitting something solid.
S&W: Smith & Wesson

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Next, let's consider the most "mainstream" of the handgun rounds. These are the rounds most likely to be found in any Wal-Mart, general store, or small gun shop, arranged by size:

.22 LR
.25 ACP
.32ACP
.380 ACP
.38 Special
.357 Magnum
9mm
.40 S&W
.44 Magnum
.45 ACP

The above calibers should be present in pretty much any store that sells ammunition anywhere in the US. There are dozens upon dozens of handgun rounds out there, but these are the "Top Ten" if you will, the best sellers currently available. Temporary shortages aside (.380ACP, I'm looking at yoooouuuuu), all of these calibers should be relatively easy to purchase. For a new shooter (someone new to the shooting world), I would not recommend a caliber not on this list as a "first" or "only" gun. Even the .357 Sig - which is a police-issued round - is hard to find and supremely expensive, not quite as exotic as 10mm but still on the harder side to find.

Which of the above calibers to choose is a matter of intensely heated and mostly pointless debate. For self-defense, the main idea is to have a round that will incapacitate an attacker quickly, meaning that the energy expended upon impact should be great. The downside to this, of course, is perceived recoil - how "hard" the gun feels in the hand when fired. A S&W 500 Magnum has pretty impressive stopping power for anything short of a pachyderm, but hurts to fire (both physically and financially). Too small of a round runs the risk of not incapacitating an attacker fast enough; too "hot" of a round (high muzzle velocity) may potentially penetrate too well and not do enough damage due to the speed at which the round passes through the body.

With modern ammunition, using a good hollowpoint design, anything larger than .32 ACP should be sufficient for self defense. .380 ACP and .38 Special should be +P designations (more powder for more power) for optimal self defense. While the age-old "9mm vs. .45 ACP" caliber war may rage ever onward in the annals of gunnie lore, the truth is that with modern +P hollowpoint ammunition, there's little practical difference between the two calibers.

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Price. This is intended as a general guideline based on what I've seen recently in my area. With the exception of .22LR, all prices are for 50 rounds. Where applicable, pricing is broken into FMJ ammo (like used for practice) and JHP (for defense) applications. We'll consider the above cartridges:

.22 LR - box of 500 - 550 rounds ("bulk pack") typically runs ~ $20
.25 ACP - $15 for FMJ, $25+ for JHP
.32ACP - about the same as .25 ACP
.380 ACP - $20 for FMJ, $30+ for JHP when you can find it
.38 Special - $15 for FMJ, $25+ for JHP; reloaded semi-lead wadcutters (SLWC) can be found for ~ $12
.357 Magnum - $18 for FMJ, $30+ for JHP; reloaded SLWC can be found for ~ $15
9mm - $12 for FMJ, $20+ for JHP
.40 S&W - $15 for FMJ, $25+ for JHP
.44 Magnum - $35 for FMJ, $45+ for JHP
.45 ACP - $22 for FMJ, $30+ for JHP

Obviously these prices are not absolute, but a rough idea of what exactly to expect when going to purchase ammunition for one's firearm. Price and availability of ammo should be a consideration in choosing a defensive arm - the greatest handgun in the world is a very poor club if you can't put any ammunition in it. Missing with $40/box ammo is much worse than hitting with $15/box ammo...

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Miscellany.

• .38 Special isn't .38" in diameter. It's really .357". .38 Special will fit and fire perfectly safely in a revolver chambered for .357 Magnum, but not the reverse. The rounds are specifically engineered so that the more powerful .357 Magnum cannot fit in a .38 Special-chambered revolver.
• .380 ACP is sometimes referred to as 9mm Kurtz or 9mm short. It cannot be fired in a 9mm-chambered pistol - this is quite dangerous AAMOF.
  
• What is traditionally called 9mm ammo is actually 9X19mm (19mm referring to the case length). It is sometimes called 9mm Parabellum, 9mm Luger, or 9mm NATO. It is NOT 9mm Largo or Steyr.
• As a general rule of thumb, handgun rounds are either revolver-specific (often a "rimmed" cartridge meaning that the base sticks out more than the case) or automatic-specific (straight-walled for easier loading). There are revolvers that fire 9mm or .45 ACP (using what are called moon clips, usually); there are semi-automatic pistols chambered in .38 Special, .357 Magnum, and .44 Magnum (among others). Only the .22LR is fully represented in both styles of action.

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This is obviously a most basic start to handgun calibers. We've stayed away from esoteric cartridges like the .357 SIG or the .45 GAP; we've refrained from getting into a discussion of some of the "legacy" cartridges like .45 Long Colt or .38 Super; basically, this is a bare-bones list for someone brand new to shooting in general so that they can get a quick feel for what's out there. The exclusion of your particular favorite blaster fodder does not mean it's no good; it could simply be uncommon, expensive, or both and therefore less-than-perfect for a noob.

What other calibers/items of note should be included in this discussion for the next set?

That is all.