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Thread: M1Carbine to .357Mag conversion

  1. #1
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    M1Carbine to .357Mag conversion

    So I talked to a Smith on the phone the other day; I would like to get an M1Carbine converted to .357Mag; and he was going on and on about how it'd cost me THOUSANDS of dollars.. and I'm thinking, it can't be that expensive right? New barrel, tap the gas hole; modify the bolt face, and away we go? Or am I missing something??
    Не умеете, научим. Не хотите, заставим!

  2. #2
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    twoblink,

    Yes, you are missing a few points.

    First of all, good carbine barrels are ONE PIECE! The extension on the barrel that holds the gas piston and the gas piston nut are MADE WITH THE BARREL, not separate parts.

    Second, what happens when the carbine ALMOST functions and they take the gas port ONE SIZE LARGER and it has too much gas now? You can't bush it or weld it up and re-drill it, it takes ANOTHE WHOLE NEW BARREL!

    Third, you are trying to take a firearm designed for a RIMLESS cartridge and make it work with RIMMED cartridges. That can be a MULTI-YEAR MULTI-MEGA-BUCK deal right there to get it to feed.

    Fourth, there is not all that much bolt face to work with. Many of the enlargements in past prototypes left no rim around the bolt. May not be the only reason they failed, but they are NOT out there selling.

    Fifth, WHY? You are trading one cartridge of a certain power for another of about the same power. The carbine has a 110 gr. bullet moving at about 1900 fps (govt. specs. were 1900 +/- 30 fps) out of a 16" carbine barrel. .Remington factory 357 Mag. shows a 158 gr. factory load at 1235 fps. out of a pistol, barrel length not mentioned and a 110 gr. bullet at 1295 fps out of a pistol, barrel length again not mentioned.

    The .357 Mag WILL gain some from the rifle barrel length, but I seriously doubt that it is going to gain 600 fps that it would need to equal the carbine round. That is why I was very happy to find a 110 gr. .357 Mag. load. I picked the Express Pistol and Revolver ammo instead of getting into specialty ammo.

    If you REALLY want a .357 Mag. equivalent semi-auto find you one of the old Winchesters in .351 WSL.

    Buckshot

  3. #3
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    Well, it's not quite as grim as that, but it is not a small job. There were a lot of carbines messed with and messed up back when the NRA was selling them for $20. Ackley shows the .30 Kurtz and maybe some others. I recall an old old magazine article describing one
    in a .375 wildcat.

    A carbine can be rebarrelled by cutting off the tube ahead of the gas block where it transitions to a plain round profile, reaming out the breech end to form a monobloc, and inserting a new tube of the desired caliber, held in by threads or solder or both. Redrill the gas port in very small steps.
    Open up the bolt face and rework the extractor.
    Play around with the magazine. Somebody on your other thread said a .30 magazine would hold several .357s before rim interference got to be a problem; but I think that will still be the major stumbling block. You are not likely to get a large capacity under good conditions.

    The gunsmith probably did not want to fool with an experimental project and talked scary money to discourage you without actually saying no.
    I have a few facts and a lot of opinions.

  4. #4
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    I have a MI-carbine converted to 9 MM---Iver Johnson,
    This abortion was garbage the day I purchased it.
    Don't do it..................

  5. #5
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    Abortion means to lose it Have you still got the rifle


  6. #6
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    The stock is gone & the rest is in Pieces-----------This rifle used P-35
    mag's--never worked properly.
    I would advise against a conversion.

  7. #7
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    "...New barrel..." That'd be a custom made barrel. Plus making the gas piston tube. Machining runs over $100 per hour. All of which will require proper macinists drawing$, that you will pay to have made. Even CNC machining requires drawings. For CNC you get to pay for the program to be written. Costs run up quickly.
    "...tap the gas hole..." Drill, not tap, the gas hole to be exactly the right size. There are no manuals to tell the machinist what size drill to use. It'd be strictly trial and error on your nickle.
    "...modify the bolt face..." Major modification to the bolt face and the extractor/ejector. 80 thou difference in diameter between the .357's rim and the carbine's case head. I'd be surprised if the .357 will fit at all. Has to be inside the diameter of the bolt face.
    Change the extractor/ejector to work with the larger rimmed case.
    Plus modifying the mag, hoping to get a rimmed case to feed reliably in a semi-auto rifle.

  8. #8
    Many of the enlargements in past prototypes left no rim around the bolt. May not be the only reason they failed, but they are NOT out there selling. | Concrete Contractor

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