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Thread: flat bolt vs round bolt

  1. #1
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    Dec 2010
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    Default flat bolt vs round bolt

    Hi, friends. Why is it that the later production of the M1 Carbine uses a round bolt? My Inland carbine has a flat bolt. What is the common problems with a flat bolt M1 carbine which prompted the production of round bolt? Is it true that flat bolt easily dislodges from the receiver during firing?

  2. #2
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    There were several reasons for the change to the type 3 round bolt for the carbine. In a nut shell it made for smoother operation,reduced the possibility of misfires,added to the dwell time and reduced high stress at the juntion of the bolt body and the locking lug. It also cut out some machining maybe speeding up production.

  3. #3
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    It was developed for the full auto carbine and the flat bolt was just no longer made, as the round worked well in the semi auto carbine also. The flat bolt supply was used up however.

  4. #4
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    Mostly done because the round bolt was easier to make.
    Spelling and grammar count!

  5. #5
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    Quote Originally Posted by Sunray View Post
    Mostly done because the round bolt was easier to make.
    This, actually it wasn't developed for the M2 carbine though it works better than a flat bolt in that rifle. It was quicker and took less machining then the flat bolt.

  6. #6
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    Changing the design of the bolt from flat to round had nothing to do with the M2 carbine, nor was it done to make it easier to manufacture. Tuna's answer sums up the real reasons quite well.
    Last edited by BrianQ; 01-31-2011 at 03:18.

  7. #7
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    I'm siding with Sunray and Legal Eagle on this one ...the flat bolt was designed with weight savings in mind, much as the front bevel on the trigger housing. Eventually, it was decided that the weight savings were so minor as to be insignificant, and eliminating these features greatly simplified production...and, as it turned out, the heavier bolt was a good thing operationally as well.

  8. #8
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    Quote Originally Posted by jonnyo55 View Post
    I'm siding with Sunray and Legal Eagle on this one ...the flat bolt was designed with weight savings in mind, much as the front bevel on the trigger housing. Eventually, it was decided that the weight savings were so minor as to be insignificant, and eliminating these features greatly simplified production...and, as it turned out, the heavier bolt was a good thing operationally as well.
    Do you know the differences between a flat and round bolt and the problems associated with the flat bolt design?

  9. #9
    Join Date
    Apr 2011
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    Round bolt WAS designed for select-fire carbine. It has a compound bevel on the bolt face. Early (M1) bolt would NOT work on M2 or M3.

    Source:
    TM9-1276, p. 56, fig. 32, see 'note'.

    That's the War Dept Technical Manual (Armorer's Manual). You don't want to argue with the War Dept. now, do ya'?
    Last edited by F-pin; 04-22-2011 at 07:11.

  10. #10
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    Just to add some information. The T4 Carbine was the designation of the experimental M2. It had both round and flat bolts in production. I saw serial number 456 and it had the flat bolt.

    The round bolt was around a lot before the T4 or M2 design.

    I have seen a lot of incorrect statements in TM's.
    Last edited by Bill Ricca; 04-22-2011 at 08:29.

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