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10mm SigArms Mauser M2...

Discussion in 'The 10 Ring' started by flyandscuba, May 6, 2010.

  1. I picked up a .40 S&W SigArms Mauser M2 for cheap a couple of gun shows ago. I bought a couple of extra barrels and a boat-load of magazines (CDNN has them for $3.99).

    I dropped off two of the barrels at my local gunsmith to have the chambers reamed to accept the 10mm cartridge (leaving one in .40 S&W) and I have removed the magazine spacer to allow the longer case of the 10mm ammunition to function properly in about half of the magazines.

    The pistol is built like a tank (being originally designed as a .45 platform) and the barrel is quite thick with a supported chamber, so I have no doubt the conversion will work fine. Actually, others have done the conversion before -- so I'm definitely not plowing new ground with this project.

    However, with the relatively short barrel -- I'm wondering which full power loads will do best, giving the most penetration and energy possible. I'm familiar with Double Tap, Cor-Bon and Buffalo Bore ammunition -- but is there anything else out there that is commercially produced that meets or exceeds the original Norma loadings?

    Here's a picture of another owner's successful conversion to 10mm. Definitely not the prettiest pistol out there, and somewhat an oddball with the rotating barrel -- but it was inexpensive and the conversion quite simple.


    Most likely, I'll use this as a truck gun -- or backwoods packer since it is not high value and should provide decent power against 2 and 4-legged predators.
    Last edited: May 6, 2010
  2. Kegs

    Kegs Ol 8 fingers ;)

    Oct 26, 2009
    Cold side of conus
    Pretty cool - did you have to change any springs out?

  3. The barrels are still with my gunsmith - but I plan to get a stronger recoil spring if needed.

    If anyone else is interested in doing this conversion, the barrels are available at Numrich and for right now CDNN is giving away two free mags if you buy other items. I ordered a firing pin assembly (pin & springs) for $14.99 and a Mauser pistol box for $9.99 to get the free mags just a minute ago. You can come across a used M2 for $325 or so at gunshows -- although some are on gunbroker for considerably higher prices.
    Last edited: May 7, 2010
  4. HOV


    Mar 5, 2005
    It's a great idea and I really can't think of a reason why it would not work very well. Cool!! Post pics when you get it done.
  5. I'll get some additional pics as soon as I get it back -- but they will look just like the one posted above.

    My gunsmith is going to mill off the .40 S&W marking on the converted barrels and stamp them with "10mm" as part of the process.
  6. The project is finished! I picked up my modified Mauser M2 from the gunsmith on Friday. Two barrels were converted to 10mm and one was retained as a .40 S&W. I've altered 4 magazines so far to accept the longer 10mm cartridges by removing the factory magazine spacer. In addition, I had to use a needle file to file down the middle "dimples" (used to hold the spacer in place) in order for the magazine to function properly with the 10mm ammunition.

    I'm in search mode for an appropriate holster for the pistol, but temporarily a DeSantis made for a S&W M&P works good enough for belt carry, as does the matching magazine pouch.

    The only ammunition I have so far is Hornady 180gr. JHP XTP. It functions fine and seems to produce no more recoil than +P 45 ACP in my other Mauser M2. The gunsmith tested both barrels with Blazer ammunition and reported 100% function. He liked the project and is on the lookout for an M2 of his own to convert. I plan to get a variety pack of full power ammunition from DoubleTap to see what real 10mm power is like in this little hand cannon.

    Pictures on the way, but right now the pistol and two magazines with 31 rounds of 10mm is completely comfortable to carry under a polo shirt.
  7. agtman

    agtman 10mm Spartiate

    Feb 28, 2001
    Congrats on your successful conversion.

    Some years ago, when these M2 pistols were more plentiful, someone posted on the site about doing the same "conversion" ... but from a .45acp M2 to 10mm.

    Your type of conversion (.40 ---> 10mm) only works if the .40S&W length mags are convertable to handle the longer OAL of the 10mm cartridge. If not, you're SOL, unless you're happy with a one-shot "10mm" semi-auto. In the case of .40 M2 mags, yours worked because you can remove the spacer.

    In the aforementioned Pistolsmith example, it was a .45 M2 which the guy converted after finding an extra .40 M2 barrel, the O.D. of which apparently fit and functioned within the .45 M2 slide.

    He then had the .40 tube reamed to 10mm specs. The .45acp M2 mags also worked, length-wise, for feeding with the 10mm cartridge. In fact, the COAL of the .45acp and 10mm AUTO are nearly identical, which is not an accident. Thus, for this guy, there was no spacer issue. Also, I believe he added stronger springs.

    All this is from memory of course, but the bottom-line is that some of these odd ball conversions to 10mm are not only possible but they do work if you're careful and if your project gun's magazines can be modified to accomodate the long OAL of the 10mm cartridge.

    Last edited: May 22, 2010
  8. I have a .45 M2 as well, and considered using it for the conversion. However, the breechface on the slide is machined for the larger diameter of the 45 ACP case. Thus, I opted for modifying the .40 S&W variant due to concerns with the .45 ACP variant's extractor and breechface being able to cycle with the 10mm cases. I believe the feed lips on the mags are the same between the two variants, but the followers are not. Also, the 45 magazine is marked for 8 rounds rather than 10 in the .40/.357 -- which are also more plentiful (CDNN is giving 2 away free with each order right now).

    All in all, it seemed easiest to modify the .40 S&W version in this particular case. As indicated above, the unique features of the Mauser M2 in .40 using the same sized magazine as a .45 ACP with a removable spacer made the conversion possible - and easy. The plentiful magazines and extra .40 S&W barrels available at an affordable price, along with the relatively inexpensive price of most used Mauser M2s on the market made this project a good bargain.
  9. agtman

    agtman 10mm Spartiate

    Feb 28, 2001
    Again, I was going by memory from what I'd read years ago, but I think you're right: in the Pistolsmith post I saw, the guy did do the mod on a .40 M2, but somehow he mentioned using the M2 45acp mags. I remember thinking, how do the .45 mags fit the .40 M2's mag well?

    Congrats anyway. :)
  10. Gary1911A1


    Jun 14, 2005
    Ohio for now
    I assume the rotating barrel helps to slow the slide down so it doesn't batter the frame. I could see giving this a try if I ran across one in good shape at a decent price plus knew a pistolsmith who would do the work.
  11. While working in Baton Rouge today, I stopped by Precision Shooting Range to put 100 rounds of Blazer ammo through the 10mm M2. Zero malfunctions through all 100 rounds. It creates quite a "boom" factor at the range. The unique pistol garnered a little attention from the employees at the range... Several asked "what is it?"

    I ran the last 50 rounds through one target pictured below -- standing, off-hand slow fire at 15 feet. I'm still getting used to the trigger pull and I had to adjust my point of aim to the upper right edge of the "10 ring" in order to get the group below. Overall, I am pleased with the function and operation of the pistol. I might have to experiment with the sights a bit if it continues to group low left with the other barrel.

    The rotating barrel lock-up and the standard factory recoil spring soaked up the recoil just fine. Ejected cases were deposited just a couple of feet behind my right shoulder. This is definitely a "keeper"! The over-engineered nature of the .40 caliber version of this short-lived offering from Sig Arms is ideal for a compact 10mm pistol. Sig Sauer produces no 10mm firearms. Maybe they should dust off this design and reintroduce it in 10mm and possibly 400 CorBon for the "cult" enthusiasts...

    I'll put an order in for a 200 round ammo variety pack from Double Tap, and I picked up two boxes of CorBon DPX for carry purposes. Maybe Oldgranpa can be convinced to engage in one more wetpack test with me for this hand cannon... ;)


    Jay's Guns II in Pensacola, FL will ream the chamber on the .40 barrel to accept the 10mm cartridge for $65.
  12. agtman

    agtman 10mm Spartiate

    Feb 28, 2001
    Wow! :wow: Very nice work. :cool:
  13. cb_98


    Jun 2, 2010
    Did you actually end up changing out any of the springs? If so please let us know what. Very interested in doing much the same as you have. Thanks.
  14. Changed no springs. Simply took the spacer out of the magazine & dropped in the reamed barrel - it was that simple!
    Last edited: Jun 3, 2010
  15. steelvipersedg

    steelvipersedg 10mm Rules!

    Dec 21, 2007
    Central NY
    :poke: Sorry to bring a thread back to life but...

    I just found this thread a little while ago and was wondering what smith did your work. I am trying to get the same thing done.

    I talked to the president of Elite Ammo (the first to convert the M2) and he said the smith he used doesn't do work anymore. :crying:

    :bowdown:Here is hoping you can help.
  16. Contact:

    Jay's Guns & Accessories II
    Pensacola, FL

    Ask to speak with Phil -- he did the work and is a 10mm fan.
  17. Burien


    Aug 19, 2009
    cdnn has mags for $1.99 now.. :)
  18. steelvipersedg

    steelvipersedg 10mm Rules!

    Dec 21, 2007
    Central NY

    thanks for the help. I can not wait. My M2 is in the mail to my ffl....

    Yeah and i saw the mags for $1.99 that is just sick.
  19. nickE10mm

    nickE10mm F.S.F.O.S.

    Apr 13, 2004
    Wichita, KS
    wow. i'm officially jealous. very schhhhweet. nice work there, bud.