9x19mm vs. 9x18mm

Does the 1mm of case capacity really make a difference in power between .380 and 9mm Luger?

Yes.

It has to do with case pressure, not just length.

According to the Accurate Arms load data, there is no SAAMI pressure spec for 9x18 Makarov, but factory ammo in that caliber runs about 21,600 psi. The SAAMI pressure spec for 9x19 is 35,000... and it can safely be loaded to even higher +P and +P+ pressures when used in modern 9x19 handguns in good condition.

With 9x18 you can get a 100gr bullet to about 1,040 ft/sec.
With 9x19, you can get a 127gr bullet to about 1,250 ft/sec.

First of all, the .380 ACP is NOT the 9x18mm. The 9x18mm is commonly known as the 9x18 Makarov and has a bore diameter of .365" and a max case length of 18.03mm. The .380 ACP has a bore diameter of .356" and a case length of 17.27mm. The 9x18 Makarov should not fit in a properly cut .380 ACP chamber. The .380 ACP operates at a SAAMI maximum average pressure of 17,000 C.U.P. AFAIK, there is no SAAMI standard for 9x18 Makarov but factory ammo runs in the area of 21,000-22,0000 C.U.P. 9mm Luger (9x19mm) has a SAAMI maximum average pressure of 33,000 C.U.P.

Steve, you beat me to it. Excellent response. Although I believe that Accurate rates the Makarov round in C.U.P., not PSI.

All well stated. The difference is in how the rounds are made and to MUCH different level specs for different styles of guns. Each designed to handle different pressures.

The .380 is 9x17mm or 9mm Kurz/Short/what have you.
The Makarov is 9x18 but has a bigger diameter and higher pressure than the .380
The 9mm Parabellum/Luger/etc is 9x19 and is MUCH hotter than either of the two above.

So yes 2mm's of case length can make 2 times the power because its build for it.

Shoot well.

Steve, you beat me to it. Excellent response. Although I believe that Accurate rates the Makarov round in C.U.P., not PSI.

Well, my name ain't Steve. ;)

You are right, the Accurate data is in cup, not psi. It would translate into 24,000ish psi (roughly).

Sorry, Sean. I regularly exchange messages with a Steve Smith on another board and on a different subject and apparently my CRS took over.

I edited the title to say "9x17mm" (brain fart on my part).

In that case, the difference is 2mm, not 1mm as you've posted. :D

9x19 has a wee bit more internal volume than 9x17, but is loaded to almost double the pressures (17,000 vs 33,000+ CUP). That pretty much says it all. If you tried to load a blowback .380 to 9x19 pressures you'd almost certainly blow it to bits.

Ahh... Steve Smith, Sean Smith...

Rifle nut, 10mm junkie...

It's all good! :p

9X18 is much closer to .380/9X17 than it is to 9mm Luger/9X19

When you go from 9X17 to 9X18 you get a boost in power

When you go from 9X18 to 9X19 you get an even bigger boost in power...

So 1mm of case lenght can make a pretty big differance...

9X18 is much closer to .380/9X17 than it is to 9mm Luger/9X19
Actually, it's quite a bit hotter than .380

Pretty much all the American ammo companies load the .380 and the 9mmMak to identical performance. They're really loading the 9mmMak DOWN to match .380 performance.

Some of the hotter ammo being imported these days shows the true capability of the 9mmMak.

I did the math on an old post (maybe on TFL) and with the "full performance ammo" the Mak falls almost exactly halfway between the .380ACP and the 9mm Luger in performance.

Good point.

I handload, and my handloads for my Makarov are a bit hotter than the factory loads, but the Mak doesn't seem to mind at all...