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.
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.
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 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: