Estimated reading time: 22 minutes

The world of firearms and ballistics is a complicated place. Ballistics is also a complicated science that many shooters do not understand all that well, so you can say a particular caliber is best for XYZ and there will always be someone that argues with you. While finding the absolute best cartridge for every situation can be tricky, knowing the basics is very important. 

In this article, we are going to go over everything you need to know about bullets so that you can make educated choices. There is a lot that goes into making a good cartridge, and every single part is important. So our first step is going to be understanding the basic terminology that comes with bullets and ballistics. 

Basic Bullet Terminology

We call the entire thing a cartridge, or round. Which includes a casing, primer, and bullet. A casing is what holds the smokeless gun powder, and has a primer in the bottom of it, then a bullet is inserted in the top of the casing. The primer is struck by the firing pin inside the firearm which creates a spark that ignites the gun powder inside the casing.

Casings are typically made of brass, and sometimes steel. Bullets can be made from many things, but most commonly they are made of a soft lead core and a copper jacket that covers the lead. For a complete list of firearm terms, you can look at this PDF by the Tennessee Court System.

That is about it as far as the components go. The only things that differentiate cartridges are the sizes and materials they are made of. The term caliber is used to tell the diameter of the bullet. Sometimes this is stated in inches, other times in millimeters. If it is in millimeters, the number will be followed by its abbreviation mm. For example, there is a .380 caliber, and a 9 mm caliber.

To make it even more complicated, a 9 mm cartridge can have many different variations. They make the bullet different weights, referred to by a unit called grains. Manufacturers also make bullets in different shapes for different applications. So you can really have many different looking cartridges and they are all considered 9mm because that is the diameter of the bullet.

Lastly, you may see the term ballistics thrown around a time or two. Ballistics is the study of how projectiles move while in flight. It can get fairly complicated, but unless you are a nerd like me, you do not really need to worry about it all that much. Just know that the design of a bullet and cartridge is going to affect its ballistics, AKA how it flies. 

Bullet Sizes & Calibers

There are certain calibers that we use for pistols, and certain ones we use for rifles. In general, the caliber of pistol rounds will be larger. However the overall cartridge is much smaller and holds less powder, so they go slower and have less power. 

Typically the bigger the bullet, the more power it has. Although when you get into the physics of it, the speed of the bullet actually has a lot more to do with power. That is why the fat and slow .380 does not have nearly as much power and the small and quick .223.

Another thing to look at is the grain of a bullet. I use a .308 to hunt with. My preferred .308 ammo is 165 grains. Which means the bullet weighs 165 grains(10.7 grams/0.377 ounces). However, you can find .308 cartridges that weigh anywhere between 150 and 180 grains. Each of them will shoot a little differently in your rifle too. 

As you can see there is a lot of tuning you could do with a rifle to get it just right. Plus a lighter grain bullet will go faster, have a flatter trajectory, but have more recoil. A larger grain bullet will have less recoil because it has less energy and will not go as far. 

You get the energy from the simple formula for kinetic energy, known in the firearms space as muzzle energy. The formula goes as energy = 0.5 * mass * velocity * velocity. Velocity is squared so it is the overruling variable in energy. When we make the bullet smaller, the explosion from the gun powder can make the lighter bullet go faster than a heavier one.

You can only make that comparison when looking at the same caliber. For example, a .223 is small and fast, but the giant 50 bmg is much bigger, faster, and has a ton more power, and it has confirmed kills at over a mile. The 50 bmg also has much more recoil than a .223. 

You will also notice that most pistol rounds have much less energy than rifle rounds. This is because pistols are smaller, and the recoil has to be manageable. Just imagine having a 30-30 in a pistol, you would probably break your wrist. 

Types of Bullets

There are many different types of bullets, and these bullets can even have their own variations. However here are a few of the most common types of bullets and what they are used for. 

  • Full Metal Jacket(FMJ) – this is the most common type of bullet. It has a soft lead core and a copper jacket surrounding it. These are round, or flat bullets that are normally good at penetrating. They tend to make straight wounding channels and go through live targets.
  • Hollow Point – These bullets will look like they have a crater missing in the middle. These bullets are designed to hit a target and mushroom out. This creates a lot more damage and has less penetration. These are commonly used in self defense and are very good at stopping targets.
  • Open Tip – you typically see these in rifle rounds. The open tip at the end is not large enough to function like a hollow point, but these bullets are known to be more accurate than a typical FMJ and are preferred by match shooters that shoot hundreds of yards.
  • Ballistic Tip – These are bullets that function more like a hollow point but in a rifle round. They are hollow at the tip, but commonly have a plastic insert in them. This gives them better aerodynamics but still allows them to expand on impact. These rounds are commonly used in hunting.
  • Soft Points – These rounds are made to function much like a hollow point. They have the tip of their led exposed at the end, which expands much more than the copper jacket on impact. This can be used as a lighter version of an FMJ, but if you want it to expand, ballistic tips are much better.
  • Boat Tail – Boat tail is more of a feature than a type, FMJ rifle rounds are commonly in the boat tail shape, but it is just a bullet that is narrow at the top and a base that tapers in. This helps with the aerodynamics of the bullet.

Bullets are designed so that they fly as optimally as possible, and make a deadly impact once they reach their target. There are obviously many different ways to do that, hence the many different types of cartridges. Although one common design for longer-range shooting is the G7.

There are multiple “G” designs, and each of them has a different function. It is not really all that important to know every detail about them if you are not trying to become a ballistic expert, but you should know they exist. There is the G1, G2, G5, G6, G7, G8, GL, and GS. Most of your modern bullets can fall under one of these G classifications, and it is how we look at the ballistics of the bullet. You can read more about them here.

Rimfire Vs Centerfire

The only difference between rimfire and centerfire ammunition is how the primer works. The primer is the mechanism that is hit by the firing pin which then sets off the gun powder and fires the projectile.

Rimfire ammunition fires when the firing pit hits the rim of the casing. Its primer is actually in the rim of the casing and when it is struck, it ignites. 

Rimfire rounds are known to be less reliable than centerfire ammo. Rimfire can not be used in higher pressure ammo, so you typically see it in smaller calibers like 22 long rifle. Rimfire is also cheaper to produce, so the ammo itself tends to be cheaper. Another downside about rimfire casings is that they can not be reloaded. 

Even still, these rimfire rounds are very popular for varmint hunting, as well as shooting on the range. They are small, and easy to transport as well as easy to shoot. Due to their light size and price, rimfire rounds are also very popular in the prepper community.

Centerfire ammo has its primer in the… you guessed it, center. Instead of a wide flat primer, it has a relatively small primer right in the middle that is struck by the firing pin. Centerfire ammo does a much better job under high pressure than rimfire. That is why just about every cartridge larger than .22 is a centerfire round. 

Centerfire rounds are used in almost all military applications. The main reason for this is that they are a lot more durable. To start with, their casing is a lot thicker, which makes them resistant to denting during transport. Secondly, they are less liable to go off when they are dropped. If a rimfire cartridge hits the ground just right, it will fire. 

Plus centerfire ammo can be reloaded. This is a huge plus for many shooters because it makes the cost of ammo much cheaper. You can also make your ammo a lot more custom and tune it to your exact needs. Reloading is very popular and has become an entire sub-niche in the firearms community,

A Cartridge for Everything

Seeing as there are so many different types of cartridges, there is really one(often dozens) for everything. It can be hard to pick which one is the best for you in a particular situation. So in this section let’s take a look at a few categories that are important: self defense, range shooting, and hunting.

Self Defense/Conceal Carry Bullets

Pistols are the most common type of firearm used for self defense. There are also a ton of calibers to pick from and thousands of pistols on the market. Even though there are many calibers to pick from, a few shine through when it comes to self defense.

Of course, there is not one perfect round for concealed carry. Even if I did pick one that was the best, someone somewhere would have a dozen reasons why it is not. So here are a few of the most commonly used rounds for concealed carry.

.380 ACP is a little bit of a lighter cartridge. While it has a fairly good sized bullet, the cartridge is small and has less power than most. This means it is great for making smaller pistols that are easy to conceal. Plus it also has much less recoil than your average pistol round. This smaller size and less recoil make it great for deep concealment, or normal concealment for smaller people.

9mm Luger or 9×19mm Parabellum is an extremely popular caliber to conceal carry. 9mm is actually smaller than a .380 in diameter. 9 millimeters is equal to .354 inches. However, it has a larger casing and more powder. Which makes it go faster and deliver a lot more energy to its target. 9mm handguns can oftentimes keep a slim profile and make really good conceal carry guns. Plus guns like the Glock 19 are double stacked and still not overly wide, so you can have 15 rounds in a single magazine.

.40 Smith & Wesson is a step up from the 9mm. It is not much taller, but it is fatter than the 9mm. So it has a heavier bullet and more powder in the casing. This makes it deliver much more energy to the target. All of this comes with the trade-off of a larger pistol, and less ammo capacity. .40 S&W is very popular, and I personally carry a Glock 23 (chambered in .40 S&W) on a daily basis.

.45 ACP is a hoss of a pistol round. It is much bigger than the 9mm and 40. However, in this case, the muzzle energy is not increased from 40 S&W. That fatter bullet weighs more and there is not enough powder to make it faster than a 40. Instead, the .45 ACP has a muzzle energy that is much more comparable to a 9mm. This is where the eternal 45 ACP vs 9mm debate comes from. Would you rather have a big round rip and tear, or a small round punch a hole in your target? There are thousands of guys with solid arguments on both sides of that coin.

Shooting at The Range

When you are shooting at the range, you want something that is going to be able to reliably hit your target at a distance. Of course, if you are shooting close range with pistols, I still recommend those rounds we talked about in the concealed carry section. 

With a rifle, you want a flat shooting cartridge that is not going to knock your shoulder off. You are going to be shooting this rifle many times, so a lot of recoil could leave you sore in the morning.

.223 Remington is a great round that can be found fairly easily. It is most commonly fired out of the AR-15 platform, but you can certainly get a bolt action rifle chambered in .223. When you are shooting with .223, you will have to do so at a relatively short range. The .223 is a small cartridge and it is not made to shoot a thousand yards. Although if you are shooting under 200 yards, this round is fun to shoot and easy to use. Plus it is often used to hunt vermin, which means this rifle does not have to only shoot on the range.

.243 Winchester is a great round that features very little recoil. This is a round that you can fire dozens of shots with and be completely fine. While you are definitely not shooting this thing extremely far, you can easily and reliably hit targets out to 300 yards with the .243. This is a good caliber for a beginner, as well as children. 

6.5 Creedmoor is one of the best long range calibers out there. It can be used to reach out to over 1200 yards. This cartridge has exploded in recent years and quickly became one of the most popular. It is known for shooting flat and far, which makes it easy to become very accurate with. If you want a cartridge that can handle more than you can give it, the 6.5 Creedmoor is the way to go.

.338 Lapua Magnum is a bit bigger than everything else on this list. It also does not have a problem shooting as far as a mile. It can be super fun to shoot on the range just because of how big and awesome it is. Although it can not be used for hunting in many places, and its practicality ends at the range.

Common Hunting Cartridges

Excluding the .338 Lapua Magnum, the range calibers I mentioned are also very popular for hunting. Although these calibers in the hunting section are a bit more popular and have been used for hunting for decades. 

.22 Long Rifle is probably the most common caliber in existence. Don’t quote me on that, but people have used the 22 for decades and it is very effective at putting down all types of game. While it is not viable for big game, it is good for shooting small creatures and having a ton of fun. This is also the ideal caliber to use when introducing kids into the world of hunting.

.308 Winchester is an extremely popular hunting round and it is what I personally use. It has also been used in the military for decades and is a tried and true killer. This round can shoot up to 1000 yards with ample correction, which is much farther than any hunter would ever need. Plus it is a relatively small round to have such a range. It has manageable recoil and is easily found in stores, which all makes it great for hunting.

30-06 Springfield is probably what your grandfather’s deer gun is chambered in. This is an old and big round that pretty much kicks like a mule. Although it also hits like a truck. This is a solid round that can take down any large game in North America. If you want one gun that can do it all, this is not a bad choice.

.300 Winchester Magnum is another great round that can take down a deer at very long ranges. Most hunters will never need to test the limits of the cartridge, but it is very effective out to 1200 yards. It is a good bit bigger than the 308, and packs a lot more punch. Although it also comes with a bit more recoil. Some hunters think the trade off is worth it, some hunters are wrong. Jokes aside, it is a good round that is very capable of hunting big game.

350 Legend is a round that is specifically made to play along with some of the strict hunting regulations in the midwest. It is a straight walled cartridge that can shoot about as far as any hunter needs. You can also get these in an AR platform, or bolt action. While it is not as great as some of the other cartridges on this list when there are strict regulations in place, this cartridge is usually a season saver.


Another very common type of firearm is the shotgun. Shotguns have many uses and come in many sizes. To be honest, a shotgun is a do it all kind of gun. They can be built to shoot deer over 100 yards, shoot waterfowl in the air, shoot sporting clays, and home defense. If you were only allowed to have just one gun, a shotgun would probably be the best option.

Shot Sizes & Slugs

The first thing to know about shotgun loads is that it comes in many different sizes. These sizes are referred to as “shot”. There are also three different types of shot, lead shot, buckshot, and steel shot. Steel shot is the most common, as you are not allowed to hunt waterfowl with lead shot. Lead shot is used to hunt turkeys and squirrels. Buckshot is used to deer hunt with, and cause a lot of damage.

The higher the shot number, the smaller the bb inside. For lead shot, the smallest thing you can get is a 12. This is a super small bb, but there is a whole bunch of them in one shotgun shell. Then, as the bb goes up in size, the amount of bb’s in the shotgun shell goes down. 

For lead shot, the smallest you can have is shot 12, then 9, 8.5, 8, 7.5, 6, 5, 4, 2, and BB. Those numbers do not seem to make a whole lot of sense, but just know that as the number gets smaller, the size of the bb gets bigger. Size BB is the largest size in lead shot.

However it would be too easy to have all types of shot use the same sizing system, so it is different for steel shot. The same principle still applies, the larger the number, the smaller the bb. Although in steel shot the smallest you can get is shot size 6. For the record, the size of the 6 shot in lead and steel is the same. If it is the same number it is the same size. 

Anyway, steel shot starts with size 6, then 5, 4, 3, 2, 1, Air Rifle, BB, BBB, T, F. Yes, Air Rifle is a size. Size F has a diameter of .22 inches and is just on the cusp of becoming buckshot. Although buckshot does not start until .24 inches.

Buckshot uses a little bit different naming system. Instead of “4 shot” it is “number 4 shot”. This denotes the difference in size between a steel shot 4 and a buckshot 4. Also, number is often abbreviated to No. So, buckshot goes from No.4 to No. 3, No. 2, No. 1, No. 0, No. 00, and lastly, No. 000. 

You will also hear people call No. 00 double-ought(or aught) buck and No. 000 is triple-ought buck. This comes from the word naught/nought which is an older English word that is used to describe nothingness, or the number zero. This word is not used much in America, and over the years we have dropped the n, so it is just ought/aught. We also see this in rifle rounds like the 30-06 (30 ought 6). This is probably because saying 30 6 is easily confused with 36, and 30 zero 6 sounds silly.

You can also have shotgun slugs. A slug is fired out of a shotgun shell that looks pretty much the same as the shells holding small bb’s. However, a slug round will only hold a single large slug. Normally these are 1-ounce slugs and they are used to shoot longer distances and cause a lot more damage. Of course, there is no competition with a rifle, but you can shoot much farther with a shotgun slug than you could with steel shot.

Shotgun Shell Components

Now that you have the bb’s figured out, let’s look at the rest of the shotgun shell. Instead of a full metal casing, it is made of a short casing that holds the gun powder, and a plastic casing that holds the shot. 

Inside the shotgun shell, there is another plastic bit called a wad. This wad is what holds the bb’s all together and it is fired from the gun. Once the wad exits the barrel it starts to open up. Once it opens, the bb’s are free to go every which direction they choose. This is why there is a “spread” of bb’s.

To recap, a shotgun shell has a small metal casing that holds the gun powder, a primer in the bottom to ignite the gun powder, and a plastic casing to hold a wad filled with bb’s or a slug. Once the shotgun shell is fired, the wad is shot out of the barrel, and then expands and lets the bb’s go in multiple directions forward.

A list of Rifle, Shotgun, & Handgun Calibers

This is a list of just about every caliber out there. I am sure I missed a few, but this list has a total of 451 calibers on it and covers more calibers than most people are aware of. The contents of this list came from Wikipedia, and each caliber is linked to its respective wiki page.

.17 Ackley Bee
.17 CCM
.17 Hornet
.17 Mach IV
.17 Remington
.17 Remington Fireball
.19 Badger
.19 Calhoon Hornet
.20 BR
.20 Tactical
.20 VarTarg
.204 Ruger
.22 Accelerator
.22 Hornet
.22 CHeetah
.218 Bee
.219 Donaldson Wasp
.219 Zipper
.22 Savage Hi-Power
.22 BR Remington
.22 Cheetah
.22 Eargesplitten Loudenboomer
.22 PPC
.22 Remington Jet
.22 Spitfire
.22 WCF
.220 Russian
.220 Rook
.220 Swift
.221 Remington Fireball
.22 Nosler
.22-250 Remington
.222 Remington
.222 Remington Magnum
.222 Rimmed
.223 Remington
.223 Winchester Super Short Magnum
.224 Weatherby Magnum
.224 Valkyrie
.225 Winchester
.297/230 Morris
.240 Apex
.240 Weatherby Magnum
.242 Rimless Nitro Express
.243 Winchester
.243 Winchester Super Short Magnum
.244 H&H Magnum
.244 Remington
.246 Purdey
.25 Remington
.25-45 Sharps
.25-21 Stevens
.25-25 Stevens
.25 Winchester Super Short Magnum
.250 Savage
.25-06 Remington
.25-20 Winchester
.25-35 Winchester
.25-45 Sharps
.297/250 Rook
.250-3000 Savage
.255 Jeffery Rook
.256 Gibbs Magnum
.256 Newton
.256 Winchester Magnum
.257 Roberts
.257 Weatherby Magnum
.26 Nosler
.260 Remington
.264 LBC-AR
.264 Winchester Magnum
.270 Weatherby Magnum
.270 Winchester
.270 Winchester Short Magnum
.275 H&H Magnum
.275 No 2 Magnum
.275 Rigby
.276 Enfield
.276 Pedersen
.277 FURY
.277 Wolverine
.28 Nosler
.280 British
.280 Flanged
.280 Jeffery
.280 Remington
.280 Ross
.284 Winchester
.30 Carbine
.30-06 JDJ
.30-40 Krag
.30 Newton
.30 Nosler
.30 R Blaser
.30 Remington
.30 Remington AR
.30-06 Springfield
.30 TC
.30-378 Weatherby Magnum
.30-30 Winchester
.300 AAC Blackout
.300 H&H Magnum
.300 ICL Grizzly
.300 Lapua Magnum
.300 Norma Magnum
.300 Remington Short Action Ultra Magnum
.300 Remington Ultra Magnum
.300 Rook
.300 Ruger Compact Magnum
.300 Savage
.300 Sherwood
.300 Weatherby Magnum
.300 Whisper
.300 Winchester Magnum
.300 Winchester Short Magnum
.303 British
.303 Magnum
.303 Savage
.375/303 Westley Richards Accelerated Express
.307 Winchester
.308 Marlin Express
.308 Norma Magnum
.308 Winchester
.308×1.5″ Barnes
.310 Cadet
.318 Westley Richards
.32 Remington
.32 Winchester Self-Loading
.32 Winchester Special
.32-20 Winchester
.32-40 Ballard
.32-40 Winchester
.325 Winchester Short Magnum
.327 Federal Magnum
.33 Winchester
.333 Jeffery
.338-06 A-Square
.338 Edge
.338 Federal
.338 Lapua Magnum
.33 Nosler
.338 Marlin express
.338 Norma Magnum
.338 Remington Ultra Magnum
.338 Ruger Compact Magnum
.338 Winchester Magnum
.338-378 Weatherby Magnum
.338 Whisper
.340 Weatherby Magnum
.348 Winchester
.35 Winchester Self-Loading
.35 Remington
.35 Whelen
.35 Winchester
.350 Legend
.400/350 Nitro Express
.351 Winchester Self-Loading
.350 Remington Magnum
.350 Rigby
.356 Winchester
.357 Magnum
.358 Norma Magnum
.358 Winchester
.400/360 Nitro Express
.360 No 2 Nitro Express
.360 No 5 Rook
.369 Nitro Express
.375 CheyTac
.375 Dakota
.375 Flanged Nitro Express
.375 H&H Magnum
.375 Remington Ultra Magnum
.375 Ruger
.375 SOCOM
.375 Weatherby Magnum
.375 Whelen
.375 Winchester
.376 Steyr
.378 Weatherby Magnum
.38-40 Winchester
.38-55 Winchester
.38-56 WCF
.380 Long
.40-65 Winchester
.450/400 Black Powder Express
.400 H&H Magnum
.450/400 Nitro Express
.400 Jeffery Nitro Express
.400 Purdey
.400 Whelen
.401 Winchester Self-Loading
.404 Jeffery
.405 Winchester
.408 CheyTac
.416 Barrett
.416 Remington Magnum
.416 Rigby
.416 Ruger
.416 Taylor
.416 Weatherby Magnum
.425 Westley Richards
.44 Henry
.44 Magnum
.44-40 Winchester
.444 Marlin
.45-70 Government
.45-90 Sharps
45 Raptor
.450 Bushmaster
.577/450 Martini–Henry
.450 Black Powder Express
.500/450 Magnum Black Powder Express
.450 Marlin
.450 Nitro Express
.500/450 No 1 Black Powder Express
.450 No 2 Nitro Express
.454 Casull
.500/450 Nitro Express
.450 Rigby
.450 Watts Magnum
.458×2-inch American
.458 Express
.458 HAM’R
.458 Lott
.458 SOCOM
.458 Winchester Magnum
.460 Steyr
.460 Weatherby Magnum
.461 Gibbs
.465 H&H Magnum
.500/465 Nitro Express
.470 Nitro Express
.475 Nitro Express
.475 No 2 Nitro Express
.476 Nitro Express
.50 Alaskan
.50 Beowulf
.50 BMG
.50-70 Government
.50-90 Sharps
.50-110 Winchester
.50-140 Sharps
.500 A-Square
.500 Black Powder Express
.500 Jeffery
.500 Nitro Express
.577/500 Nitro Express
.577/500 No 2 Black Powder Express
.505 Gibbs
.510 DTC Europ
.510 Whisper
.55 Boys
20/577 Alexander Henry
.577 Black Powder Express
.577 Nitro Express
.600/577 Rewa
.577 Snider
.577 Tyrannosaur
.585 Nyati
.600 Overkill
.600 Nitro Express
.700 Nitro Express
.950 JDJ
4.5mm mkr
5mm Craig
5mm/35 SMc
5.56×30mm MINSAS
5.56×45mm NATO
5.6×50mm Magnum
5.6×61mm VHSE
6mm AR
6mm ARC
6mm BR Remington
6mm Creedmoor
6mm Lee Navy
6mm Musgrave
6mm PPC
6mm Remington
6mm TCU
6mm XC
6.5-06 A-Square
6.5 Creedmoor
6.5mm Grendel
6.5-284 Norma
6.5mm Remington Magnum
6.5mm TCU
6.5×47mm Lapua
6.5×50mm Arisaka
6.5×52mm Mannlicher–Carcano
6.5×54mm Mannlicher–Schönauer
6.5×55mm Swedish
6.5×57mm Mauser
6.5×58mm Vergueiro
6.5-300 Weatherby Magnum
6.8mm Remington SPC
7×64mm Brenneke
7mm BR Remington
7×54mm Finnish
7×54mm Fournier
7×57mm Mauser
7mm-08 Remington
7mm Remington Magnum
7mm Remington Short Action Ultra Magnum
7mm Remington Ultra Magnum
7×61mm Sharpe & Hart
7mm Shooting Times Westerner
7mm Weatherby Magnum
7mm Winchester Short Magnum
7-30 Waters
7×33mm Sako
7.35×51mm Carcano
7.5×54mm French
7.5×55mm Swiss
7.5×57mm MAS
7.62×51mm NATO
7.62 Thumper
7.62×25mm Tokarev
7.62×40 Wilson Tactical
7.62×45mm vz. 52
7.63×25mm Mauser
7.7×58mm Arisaka
7.92×33mm Kurz
7.92×36mm EPK
7.92×57mm Mauser
8 mm-06
8mm Lebel
8mm Remington Magnum
8×50mmR Mannlicher
8×57mm IS
8×58mmR Danish Krag
8×60mm S
8×63mm patron m/32
8×64mm S
8×68mm S
8.5×55mm Blaser
9×57mm Mauser
9.3×64mm Brenneke
9.5×57mm Mannlicher–Schoenauer
11×59mmR Gras
11×60mm Mauser
12.7×99mm NATO
13.2×92mm Tank und Flieger
14.5mm JDJ
15.2mm Steyr
.410 bore
32 Gauge — .526 in (13.4 mm)
28 Gauge — .550 in (14.0 mm)
24 Gauge — .579 in (14.7 mm)
20 Gauge — .615 in (15.6 mm)
16 Gauge — .663 in (16.8 mm)
12 Gauge — .729 in (18.5 mm)
10 bore — .775 in (19.7 mm)
8 bore — .835 in (21.2 mm)
6 bore — .919 in (23.3 mm)
4 bore — 1.052 in (26.7 mm)
2 bore — 1.326 in (33.7 mm)
6.5mm JDJ
7.62×25mm Tokarev
7.63×25mm Mauser
7.65×21mm Parabellum
9mm Browning Long
9mm Mars
9×18mm Makarov
9×19mm Parabellum
10mm Auto
.22 Short
.221 Remington Fireball
.224 Boz
.25 ACP
.256 Winchester Magnum
.30 Herrett
.32 ACP
.32 H&R Magnum
.32 NAA
.32 rimfire
.32 S&W
.32 S&W Long
.327 Federal Magnum
.357 Magnum
.357 SIG
.38 Long Colt
.38 S&W
.38 Special
.38 Super
.380 ACP
.40 S&W
.400 Corbon
.41 Action Express
.41 Long Colt
.41 Remington Magnum
.44 AMP
.44 Magnum
.44 S&W American
.44 Special
.44-40 Winchester
.45 ACP
.45 Colt
.45 GAP
.45 Winchester Magnum
.450 Adams
.454 Casull
.455 Webley
.46 rimfire
.460 S&W Magnum
.475 Linebaugh
.476 Enfield
.480 Ruger
.50 Action Express
.50 Remington Navy
.500 Linebaugh
.500 S&W Magnum
.50 GI

A Quick Recap

Firearms and bullets can get complicated quickly, however, after a little bit of reading, I hope you have a solid idea of what you are looking at now. There is a lot of vocabulary to navigate around and plenty of words all mean the same thing. Once you understand the lingo, you can start to understand which calibers are used in what kind of firearm and which firearms are used for which purposes. 

There are also many types of bullets that all have a unique function. While there is a lot of science that goes into the shape and function of these bullets, knowing the basics is a good start. Each type of bullet and cartridge will all have different components that you can look at and immediately get an idea of what it is used for. Feel free to bookmark this guide and refer back to it if and when you need it!