ACP (or Ack-pee) Ammo Sizes

[herrwalther]

There is really little if any connection, they have no dimension in common, unlike .38 ACP and 9mm BL.

They were both invented by JMB. Within 8 years of each other and use the same bullet diameter. Yeah they were designed with entirely different purposes in mind. 38 ACP was reborn as the 38 Super and 380 ACP is still one of the most popular calibers for pocket guns in the world. But I can see how JMB was either trying to standardize 9mm bullet sizes or predicting where it was going anyway.

Companies are reluctant to put competitors' names on their products; like .38 Colt Special and .30-30.

Quite right. When I first got an old revolver from my mother in law, the ammo on the side said "38 Colt New Police." Well, what the hell is that? Research narrowed down it was just 38 S&W. But with the long time rivalry between Colt and Smith, they didn't want "their" ammo marked on a Colt. They just called flat nose bullets in 38 S&W cases as Colt New Police.

 

[Jim Watson]

But I can see how JMB was either trying to standardize 9mm bullet sizes or predicting where it was going anyway.

How is that? The .38 ACP 1900 predates all the foreign 9mms.
I read somewhere that earlyr .38 Autos and Supers had larger bores but industrial rationalization has turned it into just another 9mm; .346/.355".
Strangely, present SAAMI .38 Super bullet spec is .3560" where Luger is .3555" and .380 is .3565". Half a thou doesn't matter much when the tolerance is minus 6 thou, but there it is.

 

[herrwalther]

How is that? The .38 ACP 1900 predates all the foreign 9mms.

That is what I mean. JMB was experimenting with 9mm bullets right around the same time Georg Luger was in Vienna. The 1900 in 38ACP evolved into the 1911 we know today. The 45ACP was born out of government wanting a wider and relatively slower round.

 

[Jim Watson]

9mm is what you get when you take the bottleneck off a 7.65 Luger.
I see convergent evolution, not cross breeding.

 

[tark]

Was very common to use .38 ACP in older Largo imported guns.

I have shot many a 38. ACP round through an Astra 400, with no problem. And a Super or two I probably shouldn't have. If it is marked " 9mm & .38 " on the barrel it should accept the .405 rim of the ACP case.

It should be noted that the Largo is a pretty hot round. Wiki has it at 127gr. @ 1167 FPS. This is a step up from 38ACP ballistics (130 @ 1040 ) and only a small step down from the Super's numbers.

9mm is what you get when you take the bottleneck off a 7.65 Luger.

Nein! You forgot to mention "and shorten" Jim! LOL. the .30 luger is 21mm long.

 

[Pat Riot]

"FYI: I got that Ack-pee from a You Tube video."

I would have let it remain there. Youtubers, sheesh.

I believe it. I had a guy that worked for me say “I have a ‘9 em em’(9mm) but I think I want a 45 Ack-pee.”
I asked him if he was messing with me. He said “No, that’s what we call it back home.” He was from Ogden Utah. This is the same guy that would sing out “Yeet, Yeet” when chucking things into or into our trucks. He wanted a Hi-Point “Yeet cannon”. Nice guy but at 36 he acted like a 16 year old.

 

[Jim Watson]

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Nein! You forgot to mention "and shorten" Jim! LOL. the .30 luger is 21mm long.

Well, if you take most of the bottleneck off with a hacksaw, it IS shortened.

Of course the story is a lot more complicated than that, there were several variants before they got to DWM 480C that they sold to the German Navy and showed to the US Army.