7.8x19mm. Because, uh, Reasons.

What the world really needs is a .30-caliber pistol cartridge that, while more powerful that .32 ACP, is not so powerful that it requires a locked breech…” said no one ever. Not even me, and it’s my idea. It’s not even a new idea; the French had a .32 service cartridge that was rather similar. Hmm… better run it through the Wildcatter’s Checklist:

*Does it duplicate the performance of an existing cartridge? Check!

*Does it answer a question no one is asking? Check!

*Is it a pain in the butt to make? Check!

*Is it of dubious utility? Check!

*Will it be fun? Check!

Oh look, a perfect score! I guess we’d better get on with it then. Ladies and Gentlemen, I give you… drumroll please… the 7.8x19mm Auto!

75gr LFP and 65gr JHP versions, though I’m contemplating a 100gr bullet as standard. Have to see what I can come up with…

A couple years back someone gave me some .30 carbine brass, and it was inevitable that I’d find something to do with it sooner or later. Shortened and resized is turned out to be a pretty perfect donor-cartridge for the 7.8x19mm.

Umm… why 7.8mm? Well, because it turns out the .308 bullets are actually 7.82mm in diameter, not 7.62mm. No, I don’t get it either, but that’s the way it is. OK, why 19mm long? Because for the methods I had on-hand it was easy for me to shorten them to that length. I was shooting for 20mm and got 19 and said, “good enough.”

Of course I’ll need some way to test it, and as it happens I have a Maadi Helwan pistol converted to a .380 ACP straight-blowback already, and guess what new cartridge fits in a 9mm Helwan magazine?

Yep, the 7.8 fits in a 9mm Helwan/ Beretta M1951 magazine. It also cycles from the magazine, chambers and extracts from the .380 barrel.

OK, the 7.8 fits in the magazine, and it feeds, extracts and ejects from the .380-chambered barrel. So if I bore out the barrel, line it with a .308 barrel liner and cut the chamber for the new cartridge it just might work…

The goal here is to see if I can drive a 100gr. bullet to 1000fps. and still operate safely as a straight-blowback. This will yield 222 ft./lbs of energy at the muzzle, and the bullet’s high sectional density ought to give it excellent penetration, hopefully even with an expanding bullet.

The stock 9mm magazine positions the bullet well for feeding into the chamber, the extractor holds the case well and the ejector kicks it out. Now all I need is the right caliber barrel…

As it happens I have a short section of .308 barrel and some Speer 100gr. .308 Plinkers. I also have a .308 resizing die I use to resize .312-caliber bullets to .308 for use in my Mauser C96 broomhandle. This is a totally doable thing…

Of course the question of whether one should do a thing just because one can comes up… to which I say, ‘Why the hell not?’ It’ll be fun, and if it doesn’t work out I can always get another barrel for the Helwan and turn it back into a .380, or even get one of the new locking blocks from that fellow in Europe and restore it to 9mm.

So is this new cartridge going to set the world on fire? Uh, no. The world manifestly does not need this cartridge. I expect I will go to my grave as the only person to own a firearm chambered for it, in fact. But it will be fun, and that’s really the whole point.

Naturally whatever happens I’ll keep you posted.

Michael Tinker Pearce, 23 January 2021

2 thoughts on “7.8x19mm. Because, uh, Reasons.

  1. Rev Andrew M

    This is interesting. The old 8mm Roth Stern could also meet the ballistic requirements. The French 7.65 L is also close.

  2. Brett

    A long time ago I converted a Colt Army Special from 38 Special to .41 Colt. The original barrel was bulged because a parked bullet so I bought a 40 cal blank and a straight reamer. Fun fun fun. You couldn’t buy .41 Colt brass in those days so 30-30 cases were converted (yea, I even had to undercut and resize the case head). I built a swaging die to make heal bullets and a simple scissor action crimp die. I think I shot it on two occasions but what a fun project. I think your .32 Super Auto is way cool


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