Bullet Basics: Understanding Sizes, Types, and Calibers

Ready-to-fire cartridge-based ammunition has been around for just over 200 years, with Swiss gunsmith Jean Samuel Pauly usually credited with making the first integrated “needle-fired” round in 1808. Fast forward to 1846, and Parisian gunsmith Benjamin Houllier had begun to patent more successful rimfire and centerfire cartridges.

By the time of the Civil War, both breechloading longarms, such as the Spencer and Sharps Carbines and Henry lever-action rifles, along with revolvers such as the Smith & Wesson No. 1 were in circulation throughout the United States, all using cartridges instead of cap-and-ball black powder muzzle-loaded rounds.

Within a short generation of that conflict, most modern firearms were cartridge-based, with muzzleloaders considered today to be primitive.

One thing that is abundantly clear to all gun owners is that you should only try to load ammunition into a firearm that it is designed for.

Modern firearms make it (relatively) easy

All modern firearms will list the bullet chamber size either on the frame/receiver or the barrel. On pistols, revolvers, and rifles made in the U.S. or Great Britain, that size will typically be listed in terms of 1/100th (hundredth of an inch), a portion deemed a “caliber.”

For instance, a firearm with a quarter-inch bore will be “.25-caliber.” For pistols, revolvers, and rifles made in areas that have long been on the metric system, the bore will be in millimeters.

This rule largely converts back and forth with such general examples as 5.56mm/.223-caliber, 6.35mm/.25-caliber, 7.62mm/.30-caliber, 11.43mm/.45-caliber, and so forth.

Metric cartridges will include the case length

Added to this in metric cartridges is typically the length of the cartridge’s case. For instance, an 11.43x23mm round has an 11.43mm (.45-caliber) bullet diameter on a case that is 23mm long.

On this side of the pond, rather than specify the bullet diameter and the length of the case, we typically just label a cartridge by caliber and who invented it.

For example, instead of 11.43x23mm, Americans would call the same round a .45ACP, with the abbreviation standing for Automatic Colt Pistol. Clear as mud?

Shotguns go it alone

When it comes to shotguns, all the above logic goes out the window and is substituted in English-speaking countries with the terms “gauge” or “bore,” with both being a throwback to the days of old smoothbore muskets and fowling pieces and the size determined by a theoretical weight in pounds of the largest lead ball that could roll down its barrel, with higher numbers meaning a smaller gauge and lower numbers a larger gauge.

For example, a 12-gauge shotgun, which has a 73-caliber barrel, could accommodate a lead ball that weighed 1/12th of a pound. A 20-gauge shotgun, which has a comparatively smaller 62-caliber barrel, could only accommodate a 1/20th pound ball.

Of course, all shotguns today use plastic-hulled shells rather than one big honking lead ball, but the peculiar unit of measure holds.

One great thing about modern ammunition is that the head of the case (or bottom of the bullet, depending on which end is up) typically carries the story of what kind of load it is.

Usually, headstamps will include the caliber, manufacturer, and sometimes other relevant information such as when it was produced or if it is a special load such as with a heavy powder charge, denoted as “+P.”

To be safe, learn to understand what the headstamps mean on your ammunition and compare it to the chambering markings on the barrel or receiver of your firearm before loading.

Early 1800s-era cartridges had cases that were made of a variety of materials that matched their period. This included paper, bronze, drawn brass, and “Japanned” tin.

Today, only modern “yellow” brass remains in factory-produced cartridges while other materials such as nickel, aluminum, and steel are regularly encountered.

Brass vs. Steel vs. Nickel Cases

Brass is the most common as it yields a case that can usually be reloaded several times but can easily tarnish. Aluminum-cased cartridges are typically just seen used for target shooting loads but due to their nature when compared to copper-based brass cases, are cheaper.

Steel-cased ammunition, typically from Eastern Europe, is likewise economical but sometimes has a bad reputation of “sticking” in modern autoloaders, especially if shot in quantity.

Meanwhile, Nickel plated brass-cased ammo is used in many premium hunting and defense loads and is more corrosion-resistant, a bonus for cartridges that may be exposed to harsh elements.

On the other hand, hulls on shotgun shells have been plastic for generations, upgraded from all-brass or paper hulled shells.

When cartridges first hit the market in the 19th Century, the common bullet used was a variation of a simple lead round-nosed projectile.

This standard was maintained into the early 20th century and can still be found today– abbreviated on ammo boxes as “LRN” — and is a good choice for cheap target rounds.

Moving beyond the simple LRN

The type of bullet has diversified from that basic LRN over time. The goal being to provide better performance for a range of purposes, and includes a copper jacket over the lead bullet to cut back on fouling and yield a better aerodynamic projectile, imparting more accuracy at distance and better penetration, as the old LRN lead head deforms and lumps when it meets resistance.

Such jacketed bullets are typically referred to as having a full metal jacket, or “FMJ.”

Mmmm… expansion…

To help increase expansion (which dumps more of a bullet’s energy into the target, increasing stopping power and making them ideal defensive or concealed carry rounds) the nose of a bullet is left unjacketed and hollowed out, making the lead core mushroom.

Such rounds are typically referred to as jacketed hollow-points, or “JHP,” cartridges. Naturally, there are many other variations, but the above three or combinations of them cover most loads.

The below bullet caliber chart gives you a sense of the sizes and applications for various rifle caliber bullets.

While it’s not a complete ammo size chart — there are far too many rounds in the wild to fit them into an easy-to-read bullet size chart we’ve done our best to cover the most popular rifle calibers.

5.56 NATO/.223 Remington

“America’s Rifle,” the AR-15, of which more than 18 million are in circulation, is typically chambered in this common caliber.

Thanks in part to the ubiquitousness of the AR, the 223 Remington is one of the most popular centerfire rifle cartridges anywhere. The 5.56x45mm variation is its military version, and it is the standard issue service rifle cartridge for NATO forces (as well as many non-NATO countries) around the world.

The 223 Remington originated in the 1950s as the 222 Remington. When the US military wanted a new high-speed, small-caliber 308 Winchester replacement, Remington lengthened the 222 case and increased gun powder capacity by about 20%, leading to the creation of the 222 Remington Magnum in 1958.

While the cartridge wasn’t a hit with the military brass it was introduced commercially and lead to another stretched 222 — the 5.56x45mm in 1964. This cartridge was adopted by the military in their new M-16 rifle, setting the stage for 5.56x45mm centerfire domination.

Ranging in size from 55- to 77-grain loads, it is hyper-accurate and great for both short and long-range shooting – even in budget rifles.

While the 223 Rem and 5.56x45mm are very similar, they are not the same cartridge. For those interested, we break down the differences between these two near twins.

7.62x39mm

Developed as an intermediate cartridge in World War II, as Moscow’s answer to the German 7.92x33mm Sturmgewehr-series rifles, which the Russians were increasingly recovering on the battlefields of the Eastern Front, the 7.62x39mm was first fielded in the SKS rifle.

However, it went on to become best-known for its use in Mikhail Kalashnikov’s AK-47/AKM/RPD and RPK platforms.

A brute of a round, typically seen in about 122-grain loads, it is respected around the globe. We cover the best 7.62×39 rifles if you’re looking to set yourself up with some stopping power.

7.62 NATO/.308 Winchester

Developed in the 1950s from the Prohibition-era .300 Savage, to replace the long-serving .30-06 in U.S. military service, the 7.62x51mm cartridge went on to be adopted by NATO and just about every classic battle rifle such as the FN FAL, Beretta BM-59, and M-14, which were all chambered for it.

An incredibly popular hunting round, you’ll likely find a .308 Win on any hunt.

Offering up to a 180-grain pill, it is big medicine in a small package.

.30-06 Springfield

Developed to upgrade the short-lived Springfield .30-caliber M1903 cartridge, which was adopted with the bolt-action Mauser-style rifle of the same name, the slightly shorter 7.62x63mm Springfield .30-caliber M1906 cartridge– abbreviated to .30-06, or just “Aught Six” in gun circles, remained the U.S. military standard through 1957.

As millions of American men carried weapons chambered in the powerful caliber across two world wars and the Korean conflict and trusted it, the round used by Sergeant York and Audie Murphy endures in not only vintage American milsurp rifles but also millions of bolt guns sold to deer hunters over the past century.

Most military rifle bullet rounds hover around 150-grains while sporting offerings run up to 200.

.270 Winchester

Also developed from the .30-03 Government, although using a smaller .270-caliber bullet, the .270 Winchester has been on the market since the 1920s and is a go-to with American sportsmen for anything whitetail-sized and up.

Today, if a North American gunmaker has a bolt-action deer rifle in their catalog, you can guarantee that .270 Win is one of the options it offers.

Typical loads run about 130-grains.

6.5mm Creedmoor

A relatively new cartridge, the 6.5x48mm Hornady Creedmoor, which only dates back to 2007, has become widely popular, as evident from the available rifles chambered for this round.

Similar in size to the famed Swedish Mauser round, loved by hunters on several continents, the flat-shooting 6.5CM delivers better performance than that vintage cartridge due to having a superb ballistic coefficient, allowing it to stretch out to beyond 1,000 yards even in short-action bolt guns and AR-10s chambered for it.

Before the introduction of the Creedmoor, such distances were considered off-limits except for the best marksmen.

Typical loads run in the 130-grain range.

.30-30 WCF

The first American-made centerfire cartridge loaded with smokeless powder, the .30-30 (“thuddy-thuddy”) was first introduced with the Winchester Model 1894 in the final decade of the 19th century.

Since then, it has remained the most common chambering for lever-action rifles. Using bullets ranging from 120- to 170-grain, it is often said that “more deer are shot with a .30-30 than any other rifle” in North America.

.45-70 Government

Probably the oldest centerfire rifle round in serious production these days, this cartridge was adopted by the U.S. Army in 1870 for use in single-shot Springfield trapdoor breechloaders and originally utilized a 405-grain .45-caliber bullet over a black powder load, earning it the original designation as the .45-70-405.

Over the years, the cartridge has been upgraded with a smaller, more efficient bullet, and smokeless powder.

Today is it most seen in “cowboy guns” by Chiappa, Marlin, and Henry, still clocking in with hunters who appreciate the heavy soft point.

.35 Remington

A throwback to the days when hunters packed a lever-action carbine for hunting anything from deer to elk and bear, the big honking .35 Remington offered a fat bullet – up to 200-grains – in a package with a low enough recoil to function in a small-framed carbine.

This combo has kept the cartridge, as well as rifles that use it, in production since 1908.

While plenty of .410 and .20-gauge shotguns are sold every year, and the 16-gauge is making something of a comeback, by far the most popular shotgun is the 12-gauge, making it a common denominator when it comes to scatterguns.

With that being said, 1.75-inch mini shells, 3-inch magnum, and 3.5-inch super magnum length shells are in widespread circulation, but the standard is 2.75-inch shells, with almost all modern 12 gauges set up with a chamber to accommodate that size.

The amazing capability of the 12 is attributed to the variety of loads on the market, including less-lethal, low brass birdshot, high brass field shot, non-traditional loads such as bismuth and steel rather than lead, buckshot, slugs and exotic specialty rounds.

9mm Luger

Although long snubbed by American gun owners, likening it to a spitball compared to homegrown handgun calibers, the 9x19mm cartridge was designed in 1902 by Austrian gunsmith Georg Luger for his namesake pistol.

Immediately popular in military service – the German army adopted it just five years after it was introduced — the 9mm has been embraced in the U.S. relatively recently (in the 1960s and 70s) with advances in bullet technology that wiped away performance concerns.

It has since become the equivalent of 87-octane (if the semi-auto handgun market ran on gasoline).

Today, most law enforcement agencies in the U.S., including the FBI, depend on the cartridge, and more than 5 million 9mm pistols were made in the country in 2018 alone. Typical loads run between 115- and 147-grains.

We cover the best 9mm handguns if you’re in the market for a firearm that uses this classic round.

.40 S&W

Introduced in 1990, the .40 Smith & Wesson was designed as a pistol cartridge that combined the power of the 9mm with a higher magazine capacity than the .45ACP.

It remained the preferred choice for law enforcement and personal protection for about 25 years, until the FBI reverted to the 9mm in 2015.

Make no mistake, though, with loads ranging from 135- to 180-grains, the .40S&W is still in demand and ready to deliver.

For those interested in these cartridges, we compare the .40S&W to the 9MM here.

.45ACP

Designed in 1904 by John Browning in response to the U.S. Army’s request for a more effective handgun round, the .45 ACP is closely associated with Mr. Browning’s M1911 pistol, which remained a standard in American military service for 75 years.

The chunky cartridge, with the typical bullet weight clocking in at 230-grains, endures today and recently surpassed the .40S&W to become the no. 2 bestselling pistol round in the country, only surpassed by the 9mm.

We’ve got a list of our favorite .45 ACP pistols if you’re interested.

.38 Special

Hailing back to 1899, the .38 Smith & Wesson Special hit the market in S&W’s new Military & Police revolver just after the Spanish-American War and has been going strong ever since.

Since the 1940s, it has been the most popular wheel gun round, displacing older “cowboy” cartridges. Amazingly cheap for target use when buying unjacketed lead bullets, the .38SPL continues to clock in as a reliable self-defense round with good JHPs, especially in +P loads. Typical loads range from 110- to 158-grain bullets.

.357 Magnum

Introduced in 1934 and popularized by iconic revolvers like the Colt Python in the 1950s, the .357 Magnum is slightly longer than the older .38 Special, meaning handguns chambered for .357 can also fire the .38 Special.

The extended case of the .357 allows for greater power, even though it uses bullets similar in size to the .38.

We’ve got a guide to everything .357.

.44 Special (and Magnum)

Revolvers chambered for .44-caliber black powder loads such as .44 S&W (Russian) and .44-40 Winchester were extremely popular in the 19th Century.

By 1907, Smith & Wesson had updated this concept, introducing the smokeless powder .44 Special. With its substantial 200+ grain bullet, it became a top choice for those seeking a powerful round for serious business.

Fast forward to 1955, and the .44 got the Magnum treatment in much the same way as the .38 Special led to the .357 Magnum.

Hitting the market in 1884, the humble .22 Long Rifle rimfire round is a pipsqueak when compared to a .30-06, 5.56mm NATO, or 9mm, but it is widespread in use as a target and plinking round, for small game hunting, and, in a pinch, self-defense.

Used in rifles, pistols, and revolvers, the .22LR is about the most affordable cartridge that can be bought when it comes to the price-per-round cost.

That is something that will keep this useful little round in circulation for decades to come.

No matter the assortment of ammo you go with, be sure to keep it dry while saving on a per-round basis when you can by “buying it cheap and stacking it deep.”

And of course, if you do, consider a dedicated ammo safe to ensure your ammo can be stored safely and securely, especially over the long haul.

• Military.Wikia.Org, Jean Samuel Pauly
• Wikipedia, Pinfire Cartridge
• Ammo.com, Lead Round Nose Ammo