What's the difference between a rifle and a shotgun?

I used to think that shotguns fired, well, shot, and rifles fired solid bullets. It turns out that there are solid bullets for shotguns. Then I thought shotguns were smoothbore while rifles were, well, rifled. It turns out there are rifled shotguns. So what is the difference? Is it more of a spectrum thing with blunderbusses at one end and sniper rifles at the other and a smooth transition in the middle, or is there some hard line between the two?

Ultimately, it depends on the shape of the shell the weapon is designed to fire. Rifles are designed to shoot rounds shaped like rifle rounds, while shotguns are designed to shoot rounds shaped like shotgun shells - and both shot and solid (slug) rounds both have basically the same shape.

Shotguns are primarily designed to fire shot. If you fire shot out of a rifled barrel, you end up with a really weird shot pattern. Technically, a shotgun with a rifled barrel is a slug gun.

But then that gets you back to the same question of what is the difference between a rifle and a slug gun, doesn’t it?

It is kind of a spectrum, and while shotguns tend to have certain characteristics, there are enough rifle and shotgun variants that the dividing line between the two is usually the round that it fires, as @Alessan said. Shutgun shells are measured in “gauge” or “bore”, and it’s kind of an odd measurement in that a “12 gauge” round means that the barrel fits a round lead ball that is 1/12th of a pound. Similarly, a 20 gauge shotgun barrel fits a round ball that is 1/20th of a pound. So as the number gets smaller, the barrel gets bigger. Rifle rounds, by comparison, are typically given in their caliber, which is the diameter of the barrel measured in either inches or mm. But, there are exceptions, such as the .410 shotgun shell. Shotgun shells are typically made out of plastic with a brass or steel base. Rifle rounds are typically brass or steel and don’t contain plastic. But again, there are exceptions.

There is a similar fuzzy dividing line between muskets and rifles. Generally, a musket is a smooth bore muzzle loader. But there were rifled muskets as well. Militaries didn’t use rifles because the black powder fouled the barrels quickly, and since the round has to fit tightly enough to grip the rifling for it to be effective, it became too difficult to load rifle rounds down the muzzle after a few shots. Rifles were fine for hunting, since a hunter could pause between shots and clean the fouling out of the barrel, but soldiers on the battlefield couldn’t take a quick break to clean their muskets,so they used smooth bores. That changed in the 1840s with the invention of the Minie Ball, which despite being called a “ball” was actually bullet shaped. The Minie Ball had a hollow skirt that was small enough that the round could fit down the muzzle even with a heavily fouled barrel, but when fired, the skirt would expand and grip the rifling. To use this new round, they literally just took smooth bore muskets and did nothing else except rifle their barrels. These were then called “rifle-muskets”, which seems kinda obvious since they were muskets that had been rifled. But they continued to use the term rifle-muskets for the same pattern of weapon even when they were originally produced with a rifled barrel. The dividing line in Civil War weapons was if the weapon was as long as a smooth bore musket, then it was a rifle-musket, and if it was shorter, it was a rifle. But then after the war, they converted a lot of the muskets to use breech loading cartridges, and even though the barrel was still just as long as it had been, those were called rifles.

So what’s the difference between a musket and a shotgun from the 1700s and 1800s? I have a British infantry musket that is basically a 10 gauge shotgun. It’s a smooth bore, and basically will fire anything that will fit down the barrel. It can fire a round lead ball or it can fire shot. In fact, one of the military loads back in the day was called “buck and ball” which is a standard round musket ball combined with several shot pellets. The idea was that the round ball would be fired at one soldier, and the shot would spread out and maybe hit a couple of his buddies. If you took a standard military flintlock and put a hunting style stock on it, that’s basically what was sold as a “shotgun” back in the day. So where’s the dividing line there?

So yeah, the point is that the dividing line is often arbitrary.

In modern weapons, there is another fuzzy dividing line between rifles and pistols, which is made even more fuzzy by old and poorly written laws combined with some oddball rulings by the ATF. A rifle has a butt stock and a pistol doesn’t. But a pistol can have an arm brace, which looks a lot like a butt stock. A pistol also can’t be over 26" in total length. But the difference between a pistol and a short barreled rifle can literally be just the shape of the butt stock. For example, if you take an AR-15 rifle, but a shorter barrel on it and change out the stock for an arm brace style of butt stock, it’s now legally an AR-15 pistol.

There is such a huge variation in firearms that there are plenty of oddball weapons that straddle categories and the dividing lines are often completely arbitrary.

Having rifling does not make a weapon “a rifle”, or else there are plenty of really big rifles out there:

(that’s a 105mm tank gun)

Now I am curious.

(excellent and informative post, btw)

Good site explaining rifled slugs vs. sabot slugs.

Polygonal rifling allows shot to be used in a rifled barrel without the danger of the shot jamming in rifle grooves. Polygonal rifling was the first method of making rifles, a barrel formed with a straight polygonal cross section would be heated and twisted to form the helical pattern. I do not know if any available guns take advantage of polygonal rifling to fire both bullets and shot from the same gun.

Thanks, great post, very interesting!

Firing shot through a rifled barrel gives you a much bigger and donut shaped pattern.

Folk tales travel far and wide in the gun community. This is one of those things that everyone has heard but likely many fewer people have tried themselves.

I’d say that generally speaking, the dividing lines are typically formed by what sort of round is fired. There are traditional pistol cartridges, shotgun shells, and rifle cartridges, and they all had slightly different historical evolutions.

Pistol cartridges are typically a relatively heavy and large diameter bullet that travels relatively slowly when compared to those of rifles. A 9mm 124 grain bullet going 1100 fps is more or less typical- they vary from there.

Rifle cartridges are typically much smaller in diameter- a 7mm/.277 bullet is medium-sized for a rifle cartridge diameter, if not on the big side. The full stats for a .270 Remington would be a .277 diameter bullet weighing 150 grams, traveling at 2850 fps. So a little bit heavier (i.e. longer bullet), but a LOT faster, which means a lot more energy.

Both of these evolved out of their counterparts from the cap and ball era- pistols typically fired smaller balls with smaller powder charges, and rifles fired larger balls and larger powder charges. This was due to the typical uses and ranges that they were used at. Over time, this evolved into pistols firing larger diameter and slower rounds, and rifles firing smaller diameter and considerably faster rounds.

Shotguns had a more or less parallel evolution- they evolved from the old blunderbuss, which was effectively an old-timey muzzle-loading black powder shotgun used to hunt birds. This mostly required the ability to fire a fair-size cloud of shot (small pellets), but didn’t require a whole lot of velocity. So shotguns basically evolved to fire multiple projectiles, but didn’t need a lot of velocity, so they ended up as fairly low pressure, large bore weapons.

In terms of usage, pistols are meant for hand-held use, while rifles and shotguns are meant to be fired braced against the user’s shoulder, and are considerably longer as a result. They’re sometimes called “long guns” to distinguish them from pistols.

Of course, there’s a lot of overlap between the categories- you can fire slugs from shotguns, you can fire shot out of pistols, you can rig up a hand-held “pistol” out of an AR-15, and you could probably do something weird like fire 9mm out of an AR-15 “pistol” with a 9mm upper (although God knows why you’d want to do that). And there are a lot of sort of hybrid carbines- they’re rifle-style weapons firing pistol cartridges- a friend used to have a 357 Magnum lever action carbine. And other oddities like rifled slug-firing shotguns, which are a sort of dodge used to hunt deer in jurisdictions that don’t allow real rifles for safety reasons. (why not make a rifle that’s technically a shotgun to try to circumvent the law?)

But the main dividing characteristic is what sort of round they generally fire, as that’s going to be the main determinant of their performance.

@engineer_comp_geek covered it best, at the end of the day guns are the product of hundreds of years of tinkering, evolution and colloquial terms. There are lots of idiosyncrasies in “labeling and cataloguing” guns. For the average user not interested in the complexities the simplest thing to understand is guns sold at a typical gun store as a “shotgun” are designed to fire shells, rifles are designed to fire rifle rounds. You can get fairly down into the weeds debating some of these classifications with real hardcore gun enthusiasts.

Another interesting bastardized style weapon utilizes the aforementioned .410 shotgun shell–you can actually put a .410 shotgun shell into a chamber that will fit a .45 Colt cartridge. This allows for…interesting guns to be developed. There are a number of handguns designed for specifically this purpose–loading a .410 shell into a pistol, but the same pistol can also fire .45 Colt. Probably the most popular gun marketed this way today is the “Taurus Judge”, and there’s a bit of folklore that it is called that way because it’s the “preferred weapon for a judge to keep under their robes.” Supposedly an executive at Taurus found out that a number of judges in South Florida were using it as a preferred carry weapon under their robes. This has lead to other myths such as the one that judges frequently carry under their robes or that they are allowed to do so everywhere (they are in some places, not others, and I doubt anyone knows for sure how commonly judges carry.)

Where do carbines fit in all this?

Carbines are basically short rifles. Some of them shoot pistol cartridges. Some, like the M1 carbine, shoot dedicated cartridges that are straight-walled (like pistol cartridges) but more powerful than similar caliber pistol cartridges. Some, like todays M4 carbine, shoot rifle cartridges. The M4 is nothing less than a short version of the M16A1 rifle…

*Grains. A five ounce slug would be terrifying.

Just a typo on my part! That would be a 1.15" ball, right? Definitely terrifying.

And the recoil would be…brisk.

Carbines are basically just shortened rifles. In the 1800s, most standard infantry muskets had a shortened carbine version for use by cavalry. Naval forces used carbines a lot too, since the deck of a ship is crowded and has stuff everywhere which makes longer weapons a bit impractical.

Some shortened muskets were just called rifles, and some rifles that weren’t rifle-muskets had shorter carbine versions, so again, the dividing line gets a bit fuzzy. By the late 1800s after everyone had switched to cartridges instead of muzzle loaders, the longer version was typically a rifle and the shorter version was a carbine.

In the late 1800s and early 1900s most armies figured out that the shorter versions were accurate enough that they no longer needed the longer version, so shorter rifles became standard. They actually realized that shorter rifles were accurate enough in the Civil War but they kept the longer rifle muskets since they were still lining up and firing by ranks, and a long barreled musket makes it very difficult for the guy in the back row to accidentally shoot the guy in the front row in the back of the head.

And again it gets fuzzy. The Model 1903 Springfield is a rifle, for example, while the German K98 is a carbine (Karabiner 98 Kurz, or “carbine 98 short”) even though they are both almost exactly the same length. The K98 is a shortened version of the G98 (Gewehr 98, or “rifle 98”). The 1903 Springfield is basically just a copy of the German G98/K98 design. The parts aren’t interchangeable but the design is almost identical, to the point where the 1903 is often referred to as the “American Mauser”. And yet one is a rifle and the other is a carbine, just because the carbine version is based on a longer rifle version.

Then you’ve got things like the m1 carbine, which while it is a short and light rifle, it isn’t a shortened version of anything.

Pistol caliber carbines (often abbreviated PCC) have been a thing since the days of the old west. Ian from Forgotten Weapons does a lot of PCC competition videos on youtube. You can take out the word “probably” in that sentence. I don’t remember who, but someone does make a 9mm AR-15 carbine that uses standard Glock 9mm pistol magazines. Not my thing, but hey, to each their own.

Oh, I know! I’ve actually got an old .38-40 lever-action that was sold back in the late 19th/early 20th century as a companion to a .38-40 revolver that Marlin also made- I guess having one sort of ammo for your pistol and carbine was very useful.

I was just trying to dream up something possible, but fairly non-utilitarian with the 9mm AR pistol. I mean, what is the point of a 9mm AR pistol using a Glock magazine, instead of just using a you know, Glock?

The PCC class is popular in USPSA and IDPA competition. If you’ve got an AR15, a magazine well adapter and new upper are reasonably inexpensive. Some of the purpose built rifles are using 5" barrels with a permanently attached tube to bring it up to 16" + length and avoid the SBR tax.

Not relevant, except it’s further proof that hard lines don’t exist, and probably I’m the last person here to learn this, but in The Maltese Falcon, Miles. Archer is shot with a Webley-Fosbery, which is an automatic revolver