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Thread: Can I use a 10mm chamber reamer on 40 S&W?

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  1. #1
    Join Date
    7th August 2006
    Location
    Atlanta, Georgia
    Posts
    2,844

    Can I use a 10mm chamber reamer on 40 S&W?

    Everyone says that 40 is a short 10mm, is that really true.

    It is the only 40 barrel I ever plan to fit and I have a 10mm reamer (I do have 40 go/nogo gauges).

    Robert.
    NRA Endowment Life Member.
    The true danger is when liberty is nibbled away, for expedients, and by parts. - Edmund Burke 1777

  2. #2
    Join Date
    25th September 2006
    Location
    South of Lake Superior
    Posts
    13,015
    All I know about those two cartridges and their chambers is what's in the SAAMI specification book:

    The major & minor diameters at their stop shoulders are identical at 0.424 and 0.401 inch, respectively.

    The calculated included tapers of their chambers are very, very close to each other. The 40 S&W = 0.00518 inch/inch, included. The 10mm = 0.00514 inch/inch, included. That difference may be insignificant.

    Their freebore diameters are identical at 0.401"

    The major difference appears to be in the lengths of their freebores. The 40 S&W = 0.131 0.006 inch. The 10mm = 0.114 0.006 inch.

    While one cartridge may indeed be simply a shorter (by 0.142") version of the other, the freebore differences in the SAAMI specs tell me the chamber differences are not as simple.

    Regards
    When you can measure what you are speaking about, and express it in numbers, you know something about it; but when you cannot measure it, when you cannot express it in numbers, your knowledge is of a meagre and unsatisfactory kind. [Lord Kelvin]

  3. #3
    Join Date
    7th August 2006
    Location
    Atlanta, Georgia
    Posts
    2,844
    Hi Niemi,

    Thank you.

    I am hoping that I won't need to ream the chamber but if I do it sounds as if I might "get away" with a 10mm finish reamer.

    Robert.
    NRA Endowment Life Member.
    The true danger is when liberty is nibbled away, for expedients, and by parts. - Edmund Burke 1777

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