Reloading Press: .380 ACP (9x17mm)

The Reloading Press is an at-least-weekly feature here on Gaming Ballistic for 2016. Each week it looks at some interesting real-world cartridges and presents them with hopefully-useful information in GURPS Format.

.380 ACP (9x17mm)

The .380 ACP was another design by legend John Browning, and this one was to create a pistol that could use the blowback action, which allowed the barrel to be fixed in the frame and thus more accurate. More powerful rounds required the tilt-barrel action.

The chambering first appeared in the Colt Model 1908, and has been a fairly popular self-defense pistol ever since. More modern thoughts about the smallest caliber for self-defense being 9x19mm were definitely not in force back then, and several militaries adopted the .380ACP for handguns (as well as the even-smaller .32 caliber) prior to WW2.

After that, it was pretty much the .45ACP or the 9x19mm Luger.

There’s no deying it, though – firearms made with this cartridge can be ridiculously tiny, and it’s far easier and more effective to defend yourself with the tiny pistol in a coat or pants pocket than with the larger, more effective one you had to leave behind in your home or vehicle because it was too large to comfortably carry.

The .380 ACP, like the even-smaller .22LR, can injure and kill folks, and has been used to do exactly that for over 100 years.

Ballistic’s Calculator Inputs

Basic inputs for the calculator are as follows, selecting 95mm for the (test) barrel length.

.380 ACP
Chamber Pressure 21500 psi
Barrel bore 9 mm
Case Length 17 mm
Chamber Bore 9 mm
Barrel length 95 mm
Bullet Mass 95 grains
Aspect Ratio 1.4 L/Bore
Burn length 5.14 mm
Projectile Caliber 9 mm
Total Accelerated Mass 65 grains
Expansion Ratio 1.6 expansion
Projectile Load 1
Output Stats

The .380 APC is pretty much good for one thing, though it does that well – it’s one of the most powerful (“powerful”) rounds that you can put inside a blowback pistol action, or at least, it was that way for perhaps 100 years or so. 


  • The velocity is at the muzzle. The velocity with a 95mm test barrel is tuned to match real-world data at 270J with a 95gr FMG bullet. This is not the highest energy available, but if you’re looking for energy dump, you’re looking in the wrong place.
  • If you’re going to carry a 5″ barrel, carry something powerful. But in the 2.5″-5″ range, you’re looking at 2d pi damage, and so there really isn’t going to be a lot of variation in the stats here. Even the most powerful rounds in wiki will only do 2d+1 at 300-330J. 
  • The heaviest bullet that can be safely loaded in the .380ACP is 115gr. 85-95 gr is the usual.
I suspect that the core of the distribution – 2d with barrels from 2.5-5″, is more or less the end of the road here.

Alternate Loads

The only important alternate is going to be a JHP round for enhanced wounding. The official damage there would be 2d (0.5) pi+, which is only going to be friendly on unarmored targets. The ballistics program I use will tell you 2d-1 pi+, which is much more friendly, and explains why the round still has some adherents today in its niche of “capable of being carried in a tiny pistol.”


There are many small-frame handguns chambered in .380ACP. The first that deserves mention is, of course, James Bond’s weapon, the Walther PPK. That was not the first .380 ACP, but it’s probably the most iconic.

Other pistols include the “slimline” Glock 45, the Kahr P380, and the tiny, tiny Seecamp LWS-380, which can disappear into a palm.

The not-small category also includes the (in)famous MAC-11, which could empty a 32-round magazine in 1.6 seconds of continuous fire, likely resulting in severe damage to the buildings behind your target and the very dangerous air around and above the intended victim.

Wiki has a nice rundown of other .380ACP firearms.

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