Difference between .38 and 9mm?

What are the practical differences between a .38 calibre automatic and a 9 mm of a similar model?

Which is larger?
Which has greater muzzle velocity (assuming similar models of gun and types of ammo)?
Why the differentiation?

I don’t know anything about guns, but 9mm is approximately equal to 0.354 inches, so .38 is larger.

(I type this in fear of being corrected by a more expert writer.)

When you talk about ‘a .38’ you are generally talking about a rimmed cartridge designed to be used in revolvers. The ridge holds the cartridge in place in the cylinder.

A 9mm (or its bigger brother, the 9mm Para Bellum) has no ridge, it is an ‘ACP’ (Automatic Colt Pistol) cartridge. It has no ridge so the cartridge will fit into a magazine nicely.

While both fill a similar evolutionary niche, as smaller pistol rounds, they are distinct.

So are .38 rounds necessarily rimfire, or do they produce ACP ammo for the .38?

There is a .380 auto cartridge which is interchangeable with the 9mm Kurtz cartridge. Baretta has a nice little pistol for this cartridge.

But still ‘a .38’ is a rimed case, while a ‘9mm’ is not. You would have to specify if you wanted the other variant.

BTW, ever encounter a .32 ACP? Damn odd ammo!

Based on the stats from the Federal ammunition online catalog, for basic full-metal-jacket rounds (used for training or military use)

Muzzle velocity(f/s) ;Bullet Weight (grains / grams) ;Muzzle Bullet Kin Energy (ft-lbs).

.38 Special: 950; 130 / 8.43; 260
380 Auto: 960; 95 / 6.15; 190

9mm Parabellum
960; 147 / 9.53;300
1120; 124 / 8.04; 345

So basically 9mm is a higher power round by the numbers. When you get into more specialised loads, you can get higher power factors from 9mm.

Typically .38 rounds are most commonly used in revolvers, while 9mm are more commonly used in semi-automatic pistols, such as Glocks and Sigs.

There has been a general trend away from .38 to 9mm because the latter allows pistols that can hold more rounds than a revolver, offers higher power, and is now the standard NATO pistol round.

The 380 auto is an adaptation of the .38 round for semi-auto pistols. It is often considered the smallest caliber that can be credibly used for self defence in a semi-auto, and it is popular with people who want a low recoil and a light pistol.

Hope this is along the lines you were looking for…

Pistol rounds, in .38 are not a rimfire cartridge. They are centerfire, meaning they have a distinct primer, which is seperate from the casing (inserted into it). Rimfire cartridges are most commonly (may be wrong on this, IANAA [I am not an armorer]) .22 caliber, though there could be others.

Most .357 pistols that I am familiar with will also take some sort of .38 rounds, but you REALLY need to check this before doing so.

My Mother-in-law’s Lady Smith .357 Magnum (love a MIL with guns) also takes .38 special rounds… granted there is a WHOLE WORLD of difference between them in the shot effects, but the gun will accept, fire, and work properly with both. Not to mention the .38 special rounds are cheaper than the .357 rounds.

-Butler (not an expert, do not rely on this information to load your weapons, always check your manual, use ear and eye protection, and practice good muzzle control. Guns are not toys, treat all guns as loaded, etc, etc…)

Are you talking about the difference between 9mm Parabellum & 380 Auto, or 9mm Parabellum & 38 Special?

Some notes: 38 special is actually .357 inches. This is why you can fire 38 Special rounds out of a 357 magnum. The difference between those is case length.

380 Automatic is also .357- they just kept the 38 nomenclature.

9mm = .357 inch diameter as well.

38 special was originally an old black powder cartridge, if I’m not mistaken. That’s why it’s almost 2 inches long vs. the 19mm of the 9mm Parabellum. All that black powder had to go somewhere! It’s also a ** rimmed ** cartridge, meaning that there’s a wider rim at the rear of the case to keep it in a revolver cylinder. Many centerfire rounds are rimmed- .30-30, 44 magnum, 357 magnum, and 45-70 Govt to name a few.

Rimfire are something different- in rimfire rounds, the rim is hollow and filled up with priming compound. The gun’s firing pin will crush this hollow rim and set off the priming compound. This is simpler than centerfire primers, but only suitable for small rounds. This is why the only commercial rimfire rounds still left are the 22 caliber and 17 caliber rounds.

As for 9mm/38/380, the differences are:

38 special: 158 grain/10.23 gram bullet, 760 fps, 200 lb/ft of force

380 auto(9x17 mm): 95 grain/6.15 gram bullet, 960 fps, 190 lb/ft of force

9mm Parabellum (9x19mm) 115 grain/7.45 gram bullet, 1160 fps, 345 lb/ft of force

So, as you can tell, the 9mm Parabellum is the hottest round out of the three, and not much bigger than the 380 auto.

Just to add there is a non-Parabellum 9x18mm round for the Makarov style pistols. They do NOT work in the 9mm Para, nor vice versa. Know the difference, and do not confuse.