We are all aware of the fact that bullets come in various calibers; ie: 0.22; 0.303; 0.38; 0.45; etc.
Why is that; why were these sizes chosen?
Is there something about these specific sizes that makes them desirable; or is there some general principle involved in the sizing of bullets?
Why wouldn’t they be multiples of some base size; ie: 0.10; 0.20; 0.30, 0.50, etc, ?
Also, why are center fire cartridges banned for civilian use in some jurisdictions, but not rim fire?
Excellent question. I love this forum because these are the kinds of things you always wonder about but never really get an answer to.
I think that each caliber probably has it’s own story. I think .45 was chosen for “stopping power” and because anything bigger in a hand gun would be hard to handle. But why not .47 or .48? Is there really that much of a difference that they couldn’t have chosen one of those?
One of the reasons rifles are smaller caliber is because the smaller the bullet the more rounds you can carry for the same weight.
That’s my meager contribution but I’ll be looking forward to others.
Most of the time, a bullet’s caliber is not the same thing as the size. For example, .38 and .357 are both about .357; the main difference is that the .357 magnum cartridge is longer, and both can fit in and fire from a gun chambered in .357.
Sizing of a cartridge would involved balancing power, size of bullet/cartridge (smaller = can carry more of them), trajectory, velocity, etc. Different cartridges may favor different uses.
There is also the issue of fractions of an inch vs. metric. .223 and 5.56x45mm are essentially the same thing (there may be slight differences in practice though).
Rimfire cartridges are almost always smaller. The largest diameter one in common use is .22 Magnum. Most centerfire cartridges are more powerful, except small ones like .25 ACP. That is the reason why they’re banned, that and the jurisdictions are stupid.
ETA: As dzero says, the 5.56mm cartridge used by the AR rifles replaced a larger 7.62mm cartridge. It allows lighter weight and more ammo, but many feel that the M-16/M-4s are insufficient caliber in combat situations today.
Where are centerfire cartridges banned? Not in the U.S., certainly.
I haven’t heard anyone say this in decades. This was a big topic of discussion when the 5.56 mm cartridge was introduced back in the 1960s, but such concerns have generally been allayed.
I sure as hell wouldn’t want to be hit by a 5.56 mm bullet. The bullet tumbles through the body, producing horrific wounds. The cartridge also has sufficient velocity to easily penetrate body armor and helmets. What else do you need?
And incidentally, what is different about “combat situations today” that makes you think that the caliber is insufficient?
A lot of the reasons are simply historical. Someone invents a very successful gun with a certain caliber, and soon lots of other manufacturers will make guns with the same caliber simply because there are so many of those bullets on the market. After a while, even after they stop making the original gun, the caliber will be used because so many other weapons use it, and ammunition is cheap and easy to find.
Talked to any soldiers lately? I think you would be hard pressed to find an infantryman who doesn’t think that the 5.56 lacks stopping power. Yes, it tumbles and can penetrate most armor, however current US issue body armor and helmets will stop a 5.56, but not a 7.62, and I have heard many stories about enemies being shot 3-4 times with a 5.56 and continuing to fight.
The 5.56 is a good strategic round, it maims rather than kills, taking more soldiers out of the fight (“Every enemy you wound takes two more out of the fight”), but the 7.62 is a better tactical round, it puts the enemy on the ground and he doesn’t get up.
The 5.56x45mm NATO round doesn’t usually tumble unless it hits bone or enters at an oblique angle. The round will defeat most soft body armor (through Type IIIA); however, the maximum effective range is significantly less than the 7.62x51mm NATO, and its penetration effectiveness against light cover (plywood or drywall) is significantly less. Given that the 5.56x45mm is employed on the modern battlefield in what are frequently urban or close range conditions, the lack of range is not too often a limitation, and the lack of penetration power can be seen as beneficial in limiting incidental casualties. However, many active operators and law enforcement special tactics officers feel that the 5.56mm is too limited, and a round called the 6.8 SPC Remington is an intermediate round that was developed to address this issues.
The banning of centerfire cartridges, if true, is probably of European or South American origin, where many calibers are banned if they are used by the military, which results in rounds like the 9x21mm IMI that are ballistically virtually identical to the 9x19mm Parabellum. The only thing unique about centerfire rounds (other than being easy to reload) is that the primer ignites the main charge more evenly.
As for why there is the disparate array of different caliber sizes (and within most nominal calibers, there are a variety of bullet weights, cartridge lengths, and different powder loadings), you have to recognize that cartridges were developed or evolved over decades by a variety of different innovators or companies. Each cartridge specification has a unique history behind it that often doesn’t make sense at first (i…e why the .38 caliber bullets are 0.357 to 0.358 inches in diameter) but makes sense once you understand the history (that the bullet from which the modern .38 is developed originally fit the case outer diameter and was roughly 0.38 in diameter. This makes it seem (and indeed, often is) arbitrary.
A strictly linear increment may not make a lot of sense, however, even if you were starting from scratch to make a new a family of calibers. Energy depends on mass and velocity squared, and several factors govern the reliability and effectiveness of a round.
Stranger
Fackler’s work indicates that the M16A1 and M16A2 will tumble after travelling 4-5 inches through flesh. When fired from a weapon with a 20" or longer barrel, the bullets tend to fragment dramatically after tumbling if the range is less than 100 yards, and often still breaks in half at ranges between 100 and 200 yards.
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That’s not true at all. Current US Issue body armor will stop multiple hits from Armor Piercing 7.62 rounds. The helmets offer less protection of course, with a V-50 rating somewhere around a 9mm projectile at 2100fps. So basically, if a piece of shrapnel the size of a 9mm bullet is traveling at 2100fps, it will fail to penetrate 50% of the time. Slower velocites, different angles, different sizes and materials of the shrapnel will all effect your survivability.
So the body armor will stop 5.56 and 7.62, and even 7.62 AP rounds. But the helmet usually won’t stop any of those.
This is mostly myth. The tumbling thing isn’t really true, nor is the “wounding removes more men from the field” bit. 5.56 doesn’t really tumble much, as alluded to by Stranger. Its ballistic performance is pretty good, but the main advantage over 7.62 or other rounds is that you can carry more and shoot more accurately for a very small penalty in lethality.
Frankly, any round that doesn’t convert an enemy into a red mist is going to be viewed by the average infantryman as underpowered. But pretty much every modern military in the world has moved to smaller rounds because the tradeoffs are better.
As far as armor goes, we’ve never really fought an enemy that wears effective armor.
Bitches about 5.56 don’t really deserve to be taken very seriously, and are mostly the result of uninformed opinion and anecdotal evidence.
Very funny - and probably true. 
Some of it is metric vs. imperial measurement. 9mm is a nice round number, but .357 inches seems arbitrary. 0.27" is an odd value, but 7mm seems nice and round. The only exception that comes out to round numbers in both systems is the 10mm /.40cal family. which has few members.
Rifles and pistols have grooved barrels (rifling) so a bore has a major and a minor diameter, and there is no standard as to which to use, thus .30 cal. and .308 are the same, just measured differently, and of course in metric, 7.62mm seems an odd number.
Bullet weight drives a lot of the decision, and for a given shape increases as the third power of caliber, so increments of .1 inch would be far to coarse. A “normal” .38 spl bullet weighs 158 grains, while the common loading for .45 ACP is 230 grains for a similarly shaped bullet, stepping up to .50 cal. is a leap few make.
Bores and bullets need to be accurately sized to .001 inches/.02mm more or less. Beyond making it faster to write down, there is virtually no advantage to using round mubers.
Brit here, my experience of 7.62 was even if you winged them they were out of it.
Apparently you could shoot a man through a brick wall but I never did it myself.
Bearing in mind the Russians were 7.62 as well but had short rounds.
IMO the Brit Army at least got rid of the SLR because the recoil hurt peoples arms .
It sounds silly but for less motivated soldiers,they’d hold their weapons away from their shoulders when firing because the recoil hurt.
The result?
People missed completely what they were firing at.
Wasn’t the M-16 originally known as the"meat ax" in Vietnam because of the horrific wounds its rounds inflicted? Were those 5.56 or was it using a different round at that time?
The op has a good question. Why did someone way back in the past settle on a particular bullet diameter? Why did John Browning design the .45 ACP with a .452" bullet diameter? What about .459" or .473" or other diameter? Same thing with the .30-'06, or any other caliber. Someone somewhere made a bullet diameter choice. Maybe it was chosen because of manufacturing considerations, given possible machine or tooling limitations of rifling barrels many moons ago. In other words, did the ability to make internally grooved metal tubes then dictate the diameter of a bullet? Or was it the availability of rifling tooling that forced the bullet diameter choice?
The move from 7.62 down to 5.56 was probably due to the experience with the M14 rifle. It was the first US infantry rifle to have a full-auto mode, but it’s shortcomings became apparent. It had too much recoil to fire accurately in full auto mode, it was too unwieldy to use in a submachinegun role, and too lightly built to serve as a light machine gun. The US moved down to 5.56 for the M-16 to try to make full auto mode practical and to be able to carry more individual rounds. Ironically, even a 5.56 infantry rifle still couldn’t be fired accurately in full-auto and the US eventually gave up and replaced full-auto with burst mode, with a dedicated squad automatic weapon serving where needed. The M-16 was in turn replaced by the M-4, considered by many a “carbine” rather than a rifle.
The problem today is that while the 5.56 is a servicable round, many complain that the M-4 simply doesn’t have a long enough barrel to give it it’s full potential. That wasn’t critical at ranges below 300 meters but the open country US troops are fighting in in the middle east makes range important to a degree it wasn’t in Vietnam. Given that US infantry now use burst mode anyway, I’ve wondered if reviving a burst mode variant of the M-14 would be a good idea.
The .50 caliber bullets used in modern handguns are that size because if they are any larger the firearm that uses it becomes a Destructive Device and is thus required to be registered. That’s why handgun calibers top out there (.50 Action Express, .50 GI, etc.).
So in at least one case the caliber size is dictated by law.
How many infantrymen have had occasion to
I bet you’d be hard pressed to find many. If a 5.56 mm round hit you full on in the chest you’re going down like a sack of potatoes. If it goes through your femur you’ll be shrieking like a little girl and in no position to fight anyone, assuming you remain conscious, which you won’t for long.
Bear in mind combat reports of accuracy in shooting are historically overstated by a factor of at least three. You will always hear soldiers say “Jesus, I shot the guy like four times and he didn’t go down, what the hell? There’s something wrong with these bullets!” The usual explanation is that Private Bloggins just plain missed.
I would be hesitant, incidentally, to automatically assume anything a soldier says about weapons is correct. I was a soldier, and the astounding bullshit about weapons that poured from the mouths of other soldiers - and a lot of it had to be bullshit because it all contradicted each other - dwarfed the Gulf oil spill. Very few soldiers are actually experts in a multitude of weapons and well versed in weapons design and theory.
Could it explain why wounding doesn’t remove more men from the field? On its face, it makes sense: taking care of the dead is a lot simpler and less urgent than taking care of the wounded.
As dzero said upthread, every bullet type has its own story.
The general size and shape of the bullet is dictated somewhat by its use. Small rounds like the .22 are good for small game, but don’t pack enough of a wallop to reliably stop big game or a human. If you want something that hits harder, you’ve got a choice between bigger and slower or smaller and faster. Bigger slower rounds are subsonic, and don’t have the stability problems that can plague supersonic rounds, especially as they transition from supersonic to subsonic. The diameter is also only one part of the overall equation. The length and shape are also very important in the design.
There were some cases where the caliber was decided by the barrel. This usually meant that the round was being designed for an existing weapon though. For example, when they first made the Minie Ball (which is a conical bullet and not a ball at all) they simply took the Model 1840 and 1842 smooth bore muskets and rifled them. Since the existing muskets were .69 caliber (U.S. muskets were originally copies of French muskets, which were .69 caliber, and the standard stuck) this meant that the new Minie Balls had to be .69 caliber as well. In 1855 when they redesigned the muskets Another example is the .357 magnum, which was designed to be compatible with the existing .38 caliber round (the cartridge was .38, the bullet diameter was .357). The .357 and .38 super were designed to be just big enough to punch through the bullet proof vests that gangsters in the 1920s were wearing for protection. Guns that shot the new rounds had to be stronger and able to withstand greater pressures than existing .38 pistols, but the newer guns could fire both the new round and the old one, taking advantage of less expensive and readily available ammunition. The size for the .38 originally came from the metric size 9mm, which is a reasonably round number for a round roughly that size.
Generally speaking though, if you are designing everything from scratch, the barrel could be made in any diameter and did not generally dictate the size of the bullet.
The .22 was a very early cartridge, and was originally developed for indoor shooting galleries in the mid 1840s. The original cartridge was fairly low in power, and many variations, most with a bit more power, have been developed over the years. It became a very popular round and is still extremely popular because of its low cost. A lot of gun enthusiasts will do a lot of practicing with .22 rounds because they are dirt cheap, and the .22 is good for killing small game or removing pests from your farm and such. I don’t know exactly how they ended up on exactly .22 caliber, but it obviously ended up being a very good size.
.40 caliber is 10 mm, which is a nice round number, so it is easy to see how they ended up with that one.
The Colt .45 caliber was chosen because it was a replacement for earlier .50 caliber and they wanted to scale it back a little bit to make it more controllable in a pistol round. .45 is a reasonably round number that is smaller than .50 but not so much smaller that the round doesn’t have enough stopping power for what it was designed for.
That’s just a couple of examples, but you can see how every story is unique.