I've been tring to find a workable combination such as this that would headspace both on the casemouth and shoulder. Since the 357 Sig seems to work alright, then it seems to me that the 32 X 10mm would probably feed from a magazine much easier with the much lighter bullets. Any comments would be greatly apreciated. Swampdoc

I'm a fan of the 8MM bullet anyway but your project sounds like a slightly upgraded 357 Sig. It is a .357 bullet in a 40 cal case. Yours might have a little more horsepower and in my old dinosaur brain that is always a good thing but I don't think there would be an appreciable difference except in velocity. Of course I have been wrong before. It would be a nice project if you can stand the price of a custom made chamber reamer.

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I drew this cartridge up on RCBS Load. It is a pretty good looking little cartridge.
I started off with a 40 degree shoulder but after considering the case forming problems I changed it to 35 degrees.
The 357 SIG has a short neck, .150” so I gave this cartridge a neck of .2383”. This made for a balanced looking cartridge.
I put the point of the shoulder .690” up from the case head. I started the neck at .7537” and used an overall case length of .9920”
This case has a water capacity of 19.7 grains.
With a bullet seated .240” deep we have a water capacity of 15.1 grains
This leaves room for 12.7 grains of Alliant 2400 and 14.0 grains of Hodgdon Lil Gun - uncompressed.

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Let's build it on a Luger frame. I like it.

RJ

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This would be awesome in a PDW-style carbine, in a configuration similar to the upcoming Kel-Tec RMR-30. With that kind of powder capacity, it is going to want a longer barrel.

30 Carbine reinvented?

I had originally tried to form a small belt on the 223 Rem. case, make it slightly longer than the 30 Carbine, and make it in 32 caliber; but it was a lousy comprimize. So I began playing with the 10mm and necked it down slightly in a 357 Sig die, then necked it down in a bored out 30 Mauser die with a 30 degree shoulder angle, and: Viola! We now have the 32X10 or 8X10, or 32 JAG ( my initials)or whatever somebody else may want to call it. I'm not a selfish fellow, so if someone else takes the credit for it: Just send me a barrel for my Witness. Swampdoctor

I have finalized the dimentions as: Length: .992, Neck .23, Shoulder 35 Degrees, From head to shoulder: .702. The shoulder it an abrupt step in the case and it should be perfect for headspacing. Diameters: Neck .338 Shoulder .423, Head .425 . Necking the 10mm down to 32 caliber tends to cause the neck to be .338, which would be fine for headspacing alone. My goal is to begin with Hornady 60 gr. XTP HP, and work it up to about 1900 FPS if possible! But I want to also work up loads using 32-20 bullets too! I have sent my chamber prints to JGS for review.

I have finalized the dimentions as: Length: .992, Neck .23, Shoulder 35 Degrees, From head to shoulder: .702. The shoulder it an abrupt step in the case and it should be perfect for headspacing. Diameters: Neck .338 Shoulder .423, Head .425 . Necking the 10mm down to 32 caliber tends to cause the neck to be .338, which would be fine for headspacing alone. My goal is to begin with Hornady 60 gr. XTP HP, and work it up to about 1900 FPS if possible! But I want to also work up loads using 32-20 bullets too! I have sent my chamber prints to JGS for review.

I carry a BUG in NAA .32 NAA which is nothing but a .380 necked down to .32 caliber. It honestly throws a 60 gr. Hornady or Speer bullet at 1250 fps (my measured reloads and first gen Core-Bon ammo) out of a NAA Guardian pistol, which IIRC has a two inch barrel. The bullets tend to mushroom violently and penetration is reduced because of that, but it is quite a little stopper with more than enough penetration without going overboard on human sized targets. In the 10 mm case and the velocities you think you will get I would be very surprised to see those bullets hold together or get much penetration. That might be pushing those small pills a bit too fast.
Marty of Teppo Jutsu has a round based on the 10mm MAGNUM case that is necked down to .338, the .338 Spectre. It gives .357 magnum performance with bullets ranging from 160 to 300 gr. and is designed for use out of the AR-15 platform and it suppresses with with a 9mm handgun suppressor. Since the magnum case is longer than the 10mm case it may not be adaptable to a handgun as easily but it may give you some idea of what you can expect.

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I fully expect the fragile bullets which were designed for the 32 S&W Long to devastatingly destroy lots of flesh in an assailant, but I hope to work up some truly performance loads using bullets up to those which are now being made for the 327 Federal and the 32-20 Winchester. It would be great to make some bullets using 5.7 X 28 brass for jacket material, and I am in the process of trying to locate jackets for bullets of heavier construction.

I began wildcatting handgun cartridges almost thirty years ago and its just plain fun to do. I have rechambered and ruined so many guns that it isn't funny anymore: But it sure is fun! I've trimmed the 7.62X39 to 33mm, and opened it up to 40 caliber, but it just didn't do very well. I though it would make a 10mm Super, but it didn't! Maybe I'm overreaching a bit by necking the 10mm down to 7.7mm or 32 caliber, but I sincerely do believe that I'm on the right trail with this one. Plus there are plenty of guns which chamber the 10mm which could easilly be rebarreled to this cartridge.

Can't find it right now but I have also seen a 10mm Magnum parent case necked down with a .357 Sig die.

ETA: Here it is, the .357 Auto -- http://ar15barrels.com/prod/357auto.shtml

(It's Indiana deer legal BTW.)