Magazines questions

Discussion in 'M, C, L and S Series' started by 73sbVert, Oct 29, 2012.

  1. 73sbVert

    73sbVert Member

    Are the .40 and .357 magazines interchangeable? Or can you use one for the other, but not the other way around? I have both M40 and S40, and wonder what else will work. I know the M40 mags fit and work in the S40, but sticks out a fair bit.

    Also, do any other manufacturers magazines fit and can be easily modified to be used in the M40 or S40? Maybe providing more rounds? I've 'heard' that one of the S&W pistol mags work, but don't know which now. None of the Glock or Sig mags work?

    Sorry, I'll bet these questions have been asked before, but I can't seem to find them! Thanks for your help and your patience!

  2. ETH77

    ETH77 Premium Member

    The .357 SIG starts out as a .40 case, then gets necked down. They are totally interchangeable.

    As for other mags working to give more rounds, I've hacked M&P mags and added an Arredondo extension to get 19 rounds. HOWEVER, neither Big Taco nor Thaiboxer could get them to work in their arms consistantly. I shot USPSA with them and didn't have any problems in my weapons (two M40-A1s - "The Twins" which were just 7 numbers off in the serial numbers). BT measured the mags as one being longer (shorter notch position) than the Steyr notch the other shorter (longer notch position), and both were within 0.010" of the Steyr notch. That leads me to believe that there can be really subtle differences in the mag positions that make factory mags work.

    All I can say is buy a couple and try it. I just enlarged the M&P notch in mine until they stripped the snap caps out of the mag. I added a Wolff +10# spring into the mag as well.

  3. Syntax360

    Syntax360 Premium Member

    S&W Sigma .40 magazines are the "oldest" hackjob some of us have been using. You will have to cut a notch for the mag release and use Wolff springs, but the Sigma .40 magazines will work with 9mm, .40S&W, and .357SIG Steyr pistols. As with all things like this, your individual results may be mixed - sometimes the DIY mags work great and other times they hardly run w/o FTFs.