A bullet refers to the projectile portion of ammunition. There are various levels of kinetic energy transfer that are desired with the careful consideration of tradeoff to cost, recoil, weight, and more. Not every situation needs a target to be obliterated with a SLAP .50 round, but we typically want to do more than just poke holes in paper with 22LR.

What is Bullet Caliber?

A bullet caliber describes the projectile’s axial diameter in units of inches and millimeters. On a firearm barrel this can be measured as the diameter of the bore. A typical 9mm handgun or carbine has a barrel bore diameter of 9 millimeters across. A 1911 in standard .45 ACP has a barrel with a bore diameter that is 0.45 inches across.

Rimfire Vs Centerfire Ammo

Rimfire and centerfire ammunition are two of the most common cartridges you’ll find today. Both species dominate in their respective fields of focus on cost-efficiency and power, each at the expense of the other. For more information on the differences between the two types, read more about it in our previous blog Rimfire vs Centerfire Ammunition.

Rimfire

Rimfire ammunition has the advantage in ease of manufacturing, and in turn — costs. Rimfire ammo has the primer component internally surrounding the cartridge base’s rim. In the factory, this is achieved by dropping the primer in its stable liquid form down into the pre-shaped cartridge and centrifugally spun. Upon drying, the primer becomes cured and reactive to do its intended job.

For the rimfire primer to activate, the protruded ring at the cartridge base has to be able to be crushed by the firing pin. This means thin case walls, and thin case walls mean being limited to lower pressures. Consequently, rimfire ammo is limited to small calibers by pressure restrictions.

The biggest rimfire ammunition commercially available is the .17 Winchester Super Magnum which is contained in a case wall handle 33,000 psi. For the average shooter, the rimfire ammunition that you’ll most likely encounter are 22LR, 22S, .17 HMR, .17 WMR.

Centerfire

Centerfire ammunition, as the name implies, has its primer component in the center base of the cartridge. This primer component is a small cup that is inserted into a pocket with a smaller hole leading to the inside of the casing. Once struck by the firing pin, the primer detonates and ignites the powder inside of the cartridge through the smaller hole. The case wall does not have to be thin as the primer is a separate component from the casing. Thicker case walls mean higher pressure loads.

While centerfire ammunition have higher manufacturing costs, they are typically the only type of ammunition practical enough to be reloaded.

Brass vs Steel Ammo

Steel-cased ammunition has a reputation for being more cost-effective than brass-cased ammunition. Lacquered steel casings have been synonymous with the now extinct cheap Russian milsurp ammunition. While cheaper, steel is a lot stiffer than brass. In layman’s terms, it’s harder on your gun’s internals and cannot be practically resized for reloading purposes.

If you’d like to learn more about this topic, feel free to delve deeper in our blog Brass vs Steel Ammo for details.

10 Common Bullet Calibers

There’s not a sole do-it-all bullet caliber that can adjust for how much penetration and kinetic energy transfer is desired in every situation. Bullet types that are designed to fragment upon initial contact with soft tissue are at greater risk of tumbling prematurely against targets in densely wooded environments or performing poorly against body armor. Below we’ll briefly discuss the common different bullet sizes and the cartridge they’re equipped with.

.22 LR

22LR is a rimfire round that can be had in thousand round buckets without breaking the monthly budget for guns and ammo. At $0.05-0.06 per round, 22LR reigns supreme as a small, cheap staple round.

With nearly no recoil and relatively quiet shots (about on par with a nail gun going off), 22LR is an excellent gun caliber for training novice shooters. Its strength as a training tool is what fuels a market for 22LR conversion kits on gun platforms that are traditionally configured for intermediate rifle calibers.

While you most certainly won’t be taking any game worth bragging about with 22LR, it is sufficient for varmint control and taking squirrels and other small games.

9mm

9×19mm Parabellum is a classic handgun caliber that comes to mind for duty and defensive use. Widely adopted within NATO standards, you’ll be hard pressed to find most handguns without a version chambered in 9mm.

Modern powder and hollow points provide a well-balanced handgun caliber in magazine capacity and decent expansion for energy transfer into soft tissue. 9mm travels straight with speed and drops less than 2 inches when taking shots under 50 yards. Shooting 9mm delivers controllable recoil for ease of follow up shots.

.45 ACP

It’s the favorite caliber of every boomer and 1911 cult devotee, 45 ACP also called .45 Auto. The .45 ACP projectile grain is much bigger than the average 9mm bullet. The standard 230 grain with the typical .45 ACP load isn’t fast enough to exceed the sonic barrier, meaning that .45 ACP is subsonic with the exception of specialty rounds or light grains shot out of a carbine. .45 ACP is not by any means a fast round and it doesn’t need it to excel in what it’s designed for: substantial expansion into soft tissue upon entry. It is a lot easier to transfer energy into a target with more surface area, which in turn also has more kinetic energy potential.

.380 ACP

Want a handgun smaller than the average concealed 9mm but has more kinetic energy potential than 22LR? Originally designed by John Browning for blowback action, .380 ACP saw increased popularity in the mid 2000s with new life in tiny, pocket sized carry guns.

While the .380 ACP's inner case wall is the same as that of 9mm, they are nowhere near each other in ballistic performance. .380 ACP does not generate enough pressure to be considered a SAAMI caliber and is 10,000+ psi below 9mm in maximum pressure. The typical .380 ACP's penetration and expansion is comparable to that of .38 Special. If stopping a threat to your life is more important than having a handgun smaller than a P365 or a M&P Shield, it's advisable to carefully consider your options for a reliable carry gun.

7.62x39mm

In the “before” times, the SKS could be found by the barrel in front of rural gun shops without any deterrence from a passerby running off with as many as they could. After all, what kind of piss poor bloke would be driven to steal cheap milsurp like an SKS? They were plinking rifles that no one was supposed to care about if Bubba hacked off the barrel and added gaudy airsoft furniture to it.

By the end 2022, the concept of even cheap milsurp ammo is from a distant past. Mosin Nagants out price even PSA AR15s. But their legacy remains as owners of Russian guns across the nation scour for 7.62x39 within affordable range. All around the world, the AKM and its predecessor of the AK47 has been adopted in just about every country (that didn't already have their own service rifle) that the Soviet Union had ever made contact with. The Mozambique flag features the Kalashnikov pattern rifle silhouette. The design has seen widespread adoption in but not limited to Finland, Poland, Vietnam, Cambodia, Zimbabwe, Colombia, North Ireland, People's Republic of China, and many former eastern bloc states. A popular rifle needs a popular round to go with it and 7.62x39 is a well known caliber in many parts of the world for this reason.

7.62x39's .310 and .311 are characterized as fat projectiles relative to the .22 cal that 5.56 NATO uses. The 7.62x39 bullet maintains much of its muzzle velocity even when shot through short barreled firearms. While its aversion to fragmentation and tumbling is less than ideal when transferring energy to soft tissue, this trait performs as an advantage when encountering obstacles such as small tree trunks and branches while en route to its target.

.308 Winchester

Scaled down from its 30-06 parent case, .308 Winchester has held a monopoly on the big gam hunting scene until the arrival of 6.5 CD. A smaller cartridge allowed the M14 to have a greater capacity of 20 round box magazines rather than the M1 Garand's 8 round capacity. While the 1:12 twist rate of .308 Win is not better at handling heavier grain projectiles than the 1:10 twist rate of 30-06, .308 Win can handle a greater pressure than 30-06 from a maximum average pressure of 60,000 psi to 62,000 psi. .308 has earned a staple name as a common medium to big game caliber. A round good enough to drop a deer or moose is a round that can be trusted to drop a man sized target within the first hit. CZ Bren 2, IWI Galil ACE, HK G3, FN FAL, SCAR17 are examples of successful battle rifles fed in this versatile cartridge.

6.5 Creedmoor

6.5 Creedmoor was developed by Hornady for precision shooters by necking down the casing of the .30 Thompson Center. Its performance exceeds that of .308 Win in recoil mitigation, long range grouping, bullet drop. Where it falls short is currently availability. 6.5 Creedmoor has to catch up to .308 Win's well established aftermarket and projectile variety. Once manufacturers have taken initiatives to better support 6.5 Creedmoor production, we’ll see the price range begin to approach closer to 308 Win’s costs. While 308 Winchester isn’t going anywhere for a while, it’s difficult to find a new long range precision shooting rifle that doesn’t have a 6.5 Creedmoor variant. It’s obvious to see the writing on the wall of where precision long range shooting is headed.

5.56 NATO

The intermediate rifle round of the west popularized by the M4 and AR platform is as familiar to many as a defensive caliber for making reliable 300 yard hits with a full length barrel. 5.56 NATO is a nimble round known to fragment and tumble upon initial entry into soft tissue. Its immense popularity ensures that the production and aftermarket of M193 and M855 in the west is here to stay long after even your grandchildren are gone.

300 Blackout

Maneuvering a full length rifle inside a vehicle cabin and other enclosed spaces is not an easy task, and it can be burdened by the addition of a suppressor device. Military personnel that routinely fought using carbine length barrels or even shorter barrels faced the challenge of 5.56 NATO not having enough pressure build up to be as effective as Eugene Stoner originally intended. The result was having to make many more hits in critical moments before the target was no longer a threat. In response to these complaints, 300 Blackout was developed. 300 AAC BLK is a caliber meant to shine in close quarters range and suppresses much easier than 5.56 NATO. The short, midget proportioned casing of 300 Blackout encourages propellant to burn quickly and allow its .30 cal projectile to pick up speed optimally in a 9” barrel with a 1:8 twist rate. For a subsonic 300 BLK build however, the optimal twist rate becomes 1:7. To read more on the differences of subsonic 300 Blackout and supersonic 300 Blackout check out the comparison here in .300 Blackout, Supersonic vs Subsonic.

10mm

The 10mm caliber gained a reputation as the bullet caliber tried and dumped by the FBI and was popularized by the Bren Ten as well as the Colt Delta Elite. 10mm Auto is a caliber that was adopted by the FBI when they found 9mm to be insufficient for defeating body armor. It offers greater magazine capacity than .357 and even higher pressures than most factory loads. This is the handgun caliber to take with you as a defensive round capable of reliably penetrating polar bear skulls. However, having a greater pressure than .45 ACP meant handling a lot of recoil, far too much for most federal agents to take efficient follow up shots with. Consequently, lighter loads of 10mm were introduced until eventually the 10mm Lite was adapted to become 40 S&W.

Common Bullet Types

There are a variety of targets a user can face as well as obstacles that may be in the way of the target. To meet these needs we have available a wide range of projectile types.

Full Metal Jacket (FMJ)

Copper jacketed lead projectiles have been one of the earliest and longstanding projectile designs in popular use today. It is the simplest mass manufactured bullet second to only a powder coated lead casted projectile. It consists of a lead cylinder core seated into a copper cup swaged to fit the bullet’s shape.

Open Tip

Open tipped match ammunition seats the copper jacket in backwards, the opening facing the tip of the projectile rather than wrapped around the base. This opening however does not contribute to the bullet’s expansion as it contacts the target surface. The lead core is not left with an open cavity, rather only the copper jacket.

Hollow Point

High penetration isn’t desired in most home defense situations where collateral damage is a huge factor. Hollow points are designed to expand into a mushroom shape once it makes contact with its target, thereby becoming less pointy and less ideal for drilling its way out of soft tissue. They’re identified with a cavity formed in the tip of the projectile that reaches into its lead core.

Soft Point

A soft point projectile has its soft lead tip exposed purposefully. As the surface strikes the target, the tip deforms enough to help stabilize the projectile and encourages the bullet to expand. This eases transfer of kinetic energy as well as minimizes over penetration.

Ballistic Tip

At longer distances, hollow point ammunition struggles with its less aerodynamic shape. While being less pointy is ideal for when it reaches its target, it's not great for the trip to get there. A ballistic tip bullet adds a polymer point to the tip of the projectile to facilitate this.

Do Your Research!

The topic of ammunition is vast and becomes much more complicated when shooters look into making their own loads. Grain size (bullet size) and load data are subjects that require very meticulous research to turn into valuable, applicable knowledge. We hope to have interested you in getting started. If you’d like to take the next step with building out your own firearm to try out your loads or just different types of ammo that interests you, feel free to browse our lowers and uppers or contact us.