In the 9mm vs .380 question, the 9mm Luger is the stronger round. In Federal’s own factory loads, a 9mm bullet leaves the barrel about 200 feet per second faster than a .380 Auto bullet, and the 9mm is allowed to run at much higher pressure. The .380 is a shorter, milder round. Which one is right for you depends on the gun you want and how you will use it.
They are two different cartridges. They are not interchangeable, and you should never put one in a gun made for the other.
What the names mean
“9mm” and “.380” sound like different sizes, but the bullets are the same width. SAAMI’s chamber drawings list the same groove diameter for both: .355 inch, or 9.02 millimeters (SAAMI Z299.3). The real difference is the length of the case and how much powder it holds.
That is also why the two get mixed up. The bullets look alike. The cartridges are not alike, and the gun is made for one or the other.
The full name for the common 9mm is 9mm Luger. The .380 is called .380 Automatic, or .380 Auto for short. You will see both names on the box and stamped on the gun. If you want to understand what the grain number on those boxes means, read our post on what grain means in ammo.
Size: the case is shorter
SAAMI, the trade group that sets voluntary ammunition standards, publishes drawings for each cartridge. In its standard, the case for 9mm Luger is about 0.75 inch long. The .380 Automatic case is about 0.68 inch long (SAAMI Z299.3).
That is a difference of about 0.07 inch, or under 2 millimeters. It does not sound like much. But a shorter case holds less powder and takes a smaller gun.
Pressure: the 9mm runs hotter
Here is the biggest gap. SAAMI sets a maximum average pressure for each cartridge, which is the top pressure its member makers will load to. The numbers are:
| Cartridge | SAAMI maximum average pressure |
|---|---|
| 9mm Luger | 35,000 psi |
| 9mm Luger +P | 38,500 psi |
| .380 Automatic | 21,500 psi |
Source: SAAMI Z299.3, 2022. The standard prints these numbers in hundreds, as 350, 385 and 215, and says so in its notes.
So the 9mm Luger is built to handle about 13,500 psi more than the .380 Auto. That extra pressure is what lets a 9mm push a bullet faster. A gun made for one is not made to take the other’s pressure, which is one more reason never to mix them.
Speed and energy
Federal publishes muzzle velocities for its American Eagle full metal jacket loads. Here is one of each:
| Load | Bullet | Federal’s listed speed | Test barrel |
|---|---|---|---|
| 9mm Luger | 115 grain FMJ | 1,180 fps (AE9DP) | 4 inch |
| .380 Auto | 95 grain FMJ | 980 fps (AE380AP) | 3.75 inch |
The 9mm load is 200 feet per second faster, and its bullet is 20 grains heavier. The test barrels are not the same length, so this is not a perfect match. It is still a fair picture of two common loads.
We can work out the energy with the standard formula: weight in grains times speed squared, divided by 450,240. That gives about 356 foot-pounds for the 9mm load and about 203 foot-pounds for the .380 load. That is our own math from Federal’s numbers, so treat it as an estimate.
Energy is just one measure. It does not tell you how a bullet performs once it hits a target. That depends on the bullet type, and our post on FMJ vs hollow point covers that.
What the bullet weights look like
The SAAMI tables list both cartridges with many bullet weights. The 9mm Luger rows run from 88 grains up to 124 grains. The .380 Automatic rows run from 80 grains up to 95 grains. Federal sells 9mm loads up to 147 grain.
So you will see “grain” on both kinds of box, and the numbers are in different ranges. A 95 grain bullet is normal for .380 and light for 9mm. A 115 grain bullet is normal for 9mm and heavier than any .380 weight in the SAAMI tables. Read the caliber first, then the weight.
9mm vs .380: which one should you buy
Neither is right for everyone. Here is a plain way to think about it.
Think about the 9mm if:
- You want the faster, higher-pressure round.
- You want a wide choice of bullet weights. The SAAMI tables list 9mm bullets from 88 to 124 grains, and Federal sells it in 115, 124 and 147 grain loads.
- You want a pistol you can use for many jobs.
Think about the .380 if:
- You want a milder round, with lower listed pressure and speed.
- You are looking at a smaller pistol. Many small pistols are made in .380, though size depends on the exact model, so handle a few.
These are our general notes, not rules. A big .380 and a small 9mm both exist.
What to check before you buy a gun in either caliber
Run through this short list in the shop:
- Read the caliber stamped on the gun.
- Ask what ammunition the gun’s maker lists for it. The manual or the maker’s website will say, and that includes whether +P is safe in it.
- Handle the gun with an empty chamber, and work the slide and the trigger.
- Ask about ammunition for the caliber, and plan to try a couple of different weights.
- If you plan to use a range, call ahead and ask what it allows.
Taking five minutes on this now saves you from buying a gun you do not enjoy shooting.
How a gun feels in your hand
Numbers will only get you so far. The way a pistol fits your hand, how easy it is to rack the slide and how it feels when you shoot are personal. Two people can try the same gun and come away with different answers.
If you can, handle both in the shop before you decide. Pick them up. Check the grip, the trigger reach and the slide. Ask to see a few sizes and calibers side by side. We cannot tell you which one is “easy” for you, because no honest answer fits every hand.
Check the caliber every time
Whichever you buy, match the ammo to the gun. The caliber is stamped on the barrel or on the slide. Read it, then read the box. Do not guess, and do not rely on memory when you are standing in an aisle.
If you are not sure, bring the gun in or call and ask. It takes a minute and saves a lot of trouble.
Ask at the counter
Tell us what you plan to use it for and how the gun feels in your hand. We will point you to the right questions, and you can handle the guns yourself. Contact us before you drive over, or start from our home page for hours and directions.
Sources checked November 2026. Speeds are Federal’s listed numbers from test barrels of different lengths. Real speeds vary with the gun and the lot.
