What’s the Difference? Machine Gun vs. Submachine Gun

What's the difference between a submachine gun and a machine gun?

The iconic Tommy gun fires .45 caliber handgun ammunition. That makes it a submachine gun. (Shutterstock photo)

TLDR: Submachine guns use handgun ammunition. Machine guns use rifle ammunition.

If a gun-toting character pulls the trigger and holds it there while the business end goes bang-bang-bang, then there’s an excellent chance that firearm is a submachine gun or a machine gun (warning: does not apply to characters requesting someone pull their fingers). But what’s the difference between those two terms? Or is there one?

The Difference: Caliber and (sort of) Size

“Sub” comes from Latin, and means to “be under.” That should give you a hint about how “submachine guns” differ from “machine guns,” the latter of which actually comes from a Latin word meaning “to wreck some shit” (still looking for a source for that definition).

Given the “sub” definition, it’s sometimes said submachine guns are undersized versions of machine guns. That can be true, but it’s a little backward. Submachine guns use handgun ammunition, and are basically dressed up pistols. Machine guns use rifle ammunition, and are basically dressed up rifles. Rifles are larger than handguns, so naturally machine guns are larger than submachine guns.

This holds true most of the time, but it doesn’t necessarily mean every submachine gun is smaller in length or weight than machine guns.

Is the AK-47 a machine gun?

The infamous AK-47 fires 7.62 x39mm ammunition, which is roughly equivalent to the .308 rifle caliber over here in the U.S. That means the AK-47 is a machine gun, not a submachine gun. Damn metric system. (Shutterstock photo)

A Great Time to Go Generic

Writing around convoluted grammar and sentence structure is an old writer’s trick. It’s the same with submachine guns and machine guns. If you’re unsure, just pick one of those two generic terms and stick with it. Whatever point or purpose those firearms are trying to make is clear enough without getting more specific. They’re fully automatic firearms, not corn dogs.

Terminology Cheat Sheet

Here’s a quick cheat sheet to avoid some easy pitfalls with this terminology.

AR-15: Nope, the AR-15 isn’t a submachine gun or a machine gun. It’s not even an assault rifle. Read more about AR-15s here.

Assault Rifle: Many, but not all, machine guns (not submachine guns) are assault rifles. If it meets the criteria in this post, then you’re good to go.

Assault Weapon: Don’t use this term. At best, it’s vague. At worst, it introduces something politically loaded for no good reason. Read up on assault weapons in this post.

Fully Automatic Pistol/Fully Automatic Handgun/Fully Automatic Rifle: Even though they’re technically correct, I’ve not heard of “fully automatic pistol” or “fully automatic handgun” being used all that often. “Submachine gun” or “machine pistol” are the better bets. “Fully automatic rifle,” on the other hand, is a solid substitute for “machine gun.”

Machine Rifle: It’s tempting to use this term given machine guns use rifle ammunition, but writing in a “machine rifle” will probably win you a doofus award. Don’t be a doofus. Just write “machine gun.”

Referring to a “Submachine Gun” as a “Machine Gun” Upon Second Reference: I think this works. If a character is using a submachine gun on the first reference, and you call it a “machine gun” on the second reference as an abbreviated form, that’s kosher. Just don’t call it a corn dog. It’s not a corn dog.

Sub-Machine Gun vs. Submachine Gun: Pick one style and stick with it. I think “sub-machine gun” looks funky, and not in the good way like when I dance at wedding receptions. “Submachine gun” is the better of the two.

Submachine Pistol: Even though they fire handgun ammunition, substituting in “submachine pistol” for “submachine gun” is just too weird for this planet (and your fiction). However, “machine pistol” is a thing, and is covered a little later in this post.

Tactical Rifle: A good, but probably not great, catch-all for any military-esque, shouldered firearm. If you’re going for a generic depiction, pick submachine gun or machine gun and stick to it.

Machine Pistols

When submachine guns get down to handgun size, they’re sometimes called “machine pistols.” I think machine pistol is a better term than “submachine gun” at that point, even if the former is technically a subset of the latter.

That’s a Glock Model 18 in the video above, which is a great example of a machine pistol. It’s the only fully automatic model that Glock produced, although some semi-automatic models are convertible. That’s for another post. (I don’t recommend trying to do that, by the way.)

Your Characters’ Submachine Guns and Machine Guns

What kinds of bullet hoses are you assigning your characters? Leave a comment below.


Get the Book

The Writers Guide to WeaponsThe Writer’s Guide to Weapons: A Practical Reference for Using Firearms and Knives in Fiction (Writer’s Digest Books) comes with everything but the ammo. Pick up a print or digital copy from these fine retailers:

6 thoughts on “What’s the Difference? Machine Gun vs. Submachine Gun

    • Thanks, Sue! I haven’t, either, seeing as how I like to keep the weapons simple. I think a machine gun or submachine gun is too easy, unless it’s a military setting. A knife or a revolver, now the stakes seem higher.

      Liked by 1 person

  1. The AK-47’s 7.62×39 cartridge is not really equivalent to our .308; it’s actually a bit less powerful than the venerable .30-30. But it is close to being a rifle cartridge.

    Terminology quibbles: in a military context, a machine gun is likely to be a weapon that must be mounted on a tripod or other fixed mount, and it might fire a full-power .30 caliber rifle round (.30-06, .308, .303 British) or even the big .50 BMG (Browning Machine Gun). These guns are serious hardware and would be of limited value in most works of crime fiction.

    Fully automatic rifles and carbines like the AK-47, AK-74, M-16, M4 and others are nearly always selective-fire weapons (the user can opt for either semiauto or full auto) weapons, and they are often referred to as assault rifles–but this is admittedly a very sloppy phrase, and writers who want to arm their characters with one of these firearms would be well advised to do some further research in order to become knowledgeable and convey authenticity. Sidebar: such weapons are not easily available to civilians. . . .

    Liked by 1 person

    • I was about to point out what you just said: in most uses “machine gun” refers refers to a fully-automatic weapon that is designed to fill a support role. The the OP seems to give the impression that “machine gun” include assult rifles. Usually machine guns a) have large capacity( belt/drum magzing fed) b) capable of a high rate of fire c) often fitted with a bipod(light machine gun) or tripod(heavy machine gun) depending on it’s application. I am aware that some definition of machine gun such as some state law classifies assult rifles as machine guns, but people just don’t use this term that way.

      PS in a fire team, the guy who uses a machine gun is called support / support gunner / machine gunner or just gunner. Support role in a fire team is very important, because of his ability to provide heavy suppression.

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      • Indeed, AK-47 and AK-74 are assault rifles, not machine guns, though they have light machine gun “cousins”, the RPK-47 and RPK-74. In addition to what you said, assault rifles are not made for continuous fire (in particular suppression), they are too prone to overheating and other reliability issues, and are not designed to be used with tripods e.g.. One could belt-feed an AK, or feed it with a 100 round drum, for instance, but it would not be a logical choice most of the time. You are not supposed to fire more than a couple dozen rounds (e.g. 2x 20-30 round magazines) in short succession with an assault rifle. (Although there is a Youtube video of a guy shooting 300 rounds through an AK, setting it on fire.)

        Assault rifles also usually have a fire selector for single round and/or 2 or 3 round burst and/or fully automatic fire. Machine guns usually support only fully automatic fire (it’s what they are made for, and not having a fire selector means less probability of failure). Many machine guns are also designed so that the barrel can be changed quickly under battlefield conditions, if necessary due to either heat or wear, and machine gun teams often carry at least one replacement barrel.

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