Have you ever been at a local gun shop, picked up a box of 9mm full metal jacket, and gone cross-eyed looking at all the markings, numbers, and abbreviations on the box?

You’re probably not alone. Parsing the details of a box of ammo can be especially tricky, particularly for novice shooters.

This guide should help break things down.

Caliber

Caliber refers to the diameter of the projectile - the bullet, not the cartridge. Common calibers include .22, .300, 308, .45, .50, and so on and so forth.

Caliber is not the same thing as cartridge. For instance, both .22LR and .22-250 Remington are .22 caliber, but one chamber certainly cannot fire both cartridges.

Therefore, you need to know the difference between cartridge and caliber.

Cartridge

Caliber is diameter of the bore, cartridge is a specific, self-contained unit designed to feed, fire, and be ejected from a specific chamber.

For instance, .223 Remington is a specific cartridge. Any .223 Remington chamber can fire effectively any .223 Remington round.

Then you have, for instance, .50 BMG and .50 AE. These are the same caliber (.50) but very different cartridges.

There are some hybrid chamberings that can fire more than one type of cartridge, but the best way to be safe is to fire only the exact cartridge called for by the chambering.

With that said, one chambering, though it is only designed to accept one cartridge, can accept many different types of bullets.

Bullet Type

You will also note a variety of acronyms and initialisms on any given box of ammo, denoting the type of bullet loaded into the cartridge.

Some common bullet types, and their applications, are noted here:

• FMJ - Full metal jacket - Training, drilling, and target shooting
• TMJ - Total metal jacket - Training, drilling, and target shooting
• RN - Round nose (one variant is LRN, or lead round nose) - Training, drilling, target shooting
• FN - Flat nose (also called wadcutters) - Used for competition because the flat nose makes scoring easier
• JHP - Jacketed hollow point - Defensive and sporting applications
• SCHP - Solid copper hollow point - Defensive and sporting applications
• BTHP - Boat-tailed hollow point - Sporting applications like hunting
• OTM - Open-tip match - Precision and long-range shooting
• SP - Soft point - Defensive and sporting applications
• JSP - Jacketed soft point - Defensive and sporting applications
• BT - Ballistic tip - Sporting applications like hunting
• Frangible bullets - Bullets that are designed to shatter into dust on impact, making them safer for indoor range training and shooting at steel targets
• Incendiary bullets - These bullets sport a tracer that makes it possible to see the bullet’s flight with the naked eye

Bullet Weight

Bullet weight, measured in grains, is another important metric you will want to be on the lookout for. Often two rounds are basically exactly the same except in terms of bullet weight.

The heavier a bullet is, the more energy it will be able to carry, and the farther it will be able to carry it efficiently. Therefore, heavier bullets tend to be better for hunting and defensive applications (all else being equal).

It is however important to note that although heavier bullets can produce more stopping power, they also produce more felt recoil.

Muzzle Velocity

Muzzle velocity, measured in FPS (feet per second), measures how fast the bullet is moving when it leaves the muzzle.

Faster bullets tend to shoot flatter, though this is not always the case; also, heavier, slower bullets tend to have more sharply parabolic (drooping) trajectories. Some slower bullets, such as subsonic bullets, can also be unreliable in autoloading firearms.

Muzzle velocity and bullet weight are the two factors that play into another important metric, muzzle energy.

Muzzle Energy

Muzzle energy, measured in joules (J) or foot-pounds (ft-lbs), indicates how much energy the bullet is carrying when it leaves the muzzle. It is a product of bullet weight and speed, which in turn are also determined by propellant charge.

All else being equal, the higher the muzzle energy, the more stopping power a bullet will produce. However, the higher the muzzle energy the higher the felt recoil will be, too, so be aware of that.

Special Note for Shotshells

There are special things you’ll need to look for when shopping for shotshells.

Gauge

Whereas most cartridges are measured according to caliber, shotguns are denoted by gauge. The most common gauges are 12 and 20, but shotguns are still commonly produced in 10, 16, and 28 gauge. The sole exception to this rule is the .410 caliber, which is a caliber and not a gauge.

Shell Length

Shotgun chambers and receivers are graded according to their gauge and the shell length they can accommodate.

For instance, a chamber might be rated for 12 gauge 2 ¾” shells only. If that were the case, you would not be able to shoot 3” or 3 ½” shells in that chamber.

This is very important; always check the barrel stamp or receiver stamp prior to shooting, even if you know you have the gauge correct.

Type of Projectile

Shotshells are commonly loaded with shot, but they can also be loaded with:

• Slugs: Single projectiles, they may be either smooth or rifled.
• Pumpkin balls: Single, round projectiles that are like musketballs.
• Saboted bullets: Single projectiles, often jacketed, and encased in a plastic sleeve called a sabot.

Shot Size and Payload Weight

If the shell is loaded with shot, it will be either buckshot or birdshot, also known as fine shot.

Buckshot is bigger than birdshot and graded from #000 (triple-aught) buckshot, in which the projectiles are .36” in diameter to #4, in which the projectiles are .24” in diameter.

Birdshot is finer than buckshot and typically ranges from T shot (which is only a little finer than #000 buck, at .2” in diameter) to #9 birdshot, in which each pellet is only .08” across. The higher the number, the finer the shot, and the smaller the shot pellets.

Because there are many pellets typically loaded into a shell containing shot (either buck or bird) the payload is usually measured by weight in ounces rather than by the number of pellets contained. Light loads typically weigh between ½ and ¾ of an ounce, with heavier loads being an ounce or more.

Muzzle Velocity

Shotshells are also graded according to muzzle velocity, which is typically around 1000 FPS, though it could be slightly higher depending on the weight of the shot load.

We Have It All from Shotshells to 9mm Full Metal Jacket

Whether you’re here for bulk 12ga target loads or need some 9mm full metal jacket ammo for the range, we have what you need. Take a look through our collection; hopefully now that you’re ready with the insight offered by this article, you’ll be able to decipher the markings on a box of ammo like an old hand.