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Thread: 10mm to .40 s&w

  1. #1
    Boolit Master
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    10mm to .40 s&w

    does anyone cut down 10mm to .40 S&W length?

    if so any notable things to consider? (other than 10mm large primer and .40S&W small primer)

  2. #2
    Boolit Master
    marlin39a's Avatar
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    I can't imagine anybody doing this. 40S&W brass is all over the range. 10mm is not, and is expensive.

  3. #3
    Boolit Buddy
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    PM me. I’ll give you two for one. 2 40 cases for one 10mm.

    I don’t even own the 10mm yet.

  4. #4
    Boolit Buddy
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    I agree not worth the time and 10mm is in high demand now so I would just trade and save your time. I can offer you the same deal 2 x 40 for 1 x 10mm as well and you wont have to bother cutting anything down.

  5. #5
    Boolit Grand Master Outpost75's Avatar
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    Also if you cut down 10mm to .40 S&W, you also need to mouth ream them. Labor intensive.
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  6. #6
    Boolit Master maxreloader's Avatar
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    ^^^ What DanishM1Garand said... except I have 3 10mm's and can never have enough brass to feed them.
    Looking for Ideal mold 419181 (44 Evans Long)
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  7. #7
    Boolit Master
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    i'm not looking to trade...doesn't anyone actually read and comprehend each word in a sentence?

    the question was purely that...a question.

  8. #8
    Boolit Buddy BrutalAB's Avatar
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    Im sure someone does. There are a lot of people out there loading. One of them is probably in a situation where 40 s&w brass is hard/impossible to get and 10mm is easy, maybe its illegal to own a 10mm auto firearm and illegal to own 40 s&w brass.
    I dont know any of these people so cant attest to any issues they have ran into.
    Praise the Lord and pass the ammunition.

  9. #9
    Boolit Master 1006's Avatar
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    Consideration: the brass may get too thick in the case wall as you trim down the length to 40. This would cause a problem. The case mouth might swell to a diameter too large for the gun’s chamber.

    I am a 40S&W fan. Load it hot or light.

  10. #10
    Boolit Grand Master

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    Okay the 40 S&W and 10 mm are very close other than length. cutting down 10 mm to 40 S&W was the how the original testing was probably done. Things I would look at are internal case tapers the 10 mm may have a heavier taper in it and need reamed to make bullet seating room with out bulges. 10 mm is large primer and 40 data is for small pistol so loads should be dropped and worked up but not a big deal. Last that should be checked is the case head thickness heights so capacity may be lower or different

  11. #11
    Boolit Buddy
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    Quote Originally Posted by mozeppa View Post
    i'm not looking to trade...doesn't anyone actually read and comprehend each word in a sentence?

    the question was purely that...a question.
    I'm pretty sure that we did understand the question and I believe we all answered. Can it be done? Yes. Is it worth the time , effort and frustration, probably not.

    As many pointed out besides cutting those down you might have to deal with brass being too thick now so thats another step plus when its all said and done you'll end up with 40S&W brass but with large primers because 10mm uses LP and not SP primers so you'll have to develop your loads from nothing as there will be no published data for 40S&W brass with LPP.

    As I get older I realize that its easier when you dont try to reinvent the wheel but if its something that you are dying to try and have time to play with then more power to you. I wont stop you. I'm actually curious how that works out.

  12. #12
    Boolit Master KYCaster's Avatar
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    It's called the "Centimeter".
    Those crazy old IPSC guys did it way back when (that's where S&W got the idea for their .40).

    Like others have said, necks have to be reamed and the thick brass also reduces case volume, add the LP primer and high working pressure and powder selection becomes critical.

    Not really relevant to your question, but another complication at the time was the trend toward heavy-for-caliber bullets to reduce felt recoil. Those guys were launching 200 and 220 grain bullets at 900 and 820 fps to make the old 180PF. There were very few available powders at the time suitable for the task (the situation hasn't improved substantially), and there were no SAMI specs or reloading data available to guide those intrepid pioneers in their quest for the ultimate IPSC cartridge.

    Interesting times.

    Hope this helps...
    Jerry
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  13. #13
    Boolit Buddy
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    I'd think yes, similar maybe to making 9mm Makarov from 9mm Luger. Constantly amazed at the judgement introduced in responses. It's a case forming forum, making sense isn't one of the criteria. Bravo to the original poster for asking. Take it a step further, make 40 from 10 then make 45 jacketed bullets from that new case. (Geeez but jacketed bullets are available everywhere!). And as I think about it, why cast? Cracking up here on a cold Indiana morning......

  14. #14
    Boolit Master
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    for those who say "ream the case mouths"
    ....my 180 grain boolits are nearly as different from my 150 grain boolits in length as the .40 S&W is from the 10mm.

    so what i'm saying is that the 150 grain boolit would sit no deeper into a cut down 10mm case than a 180 grain boolit does in a "non cut down" 10mm case.

    so in reality ....there would be virtually the same volume under the base of the boolit ....so again, why would reaming be necessary?

  15. #15
    Boolit Grand Master

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    Quote Originally Posted by marek313 View Post
    I'm pretty sure that we did understand the question and I believe we all answered. Can it be done? Yes. Is it worth the time , effort and frustration, probably not.

    As many pointed out besides cutting those down you might have to deal with brass being too thick now so thats another step plus when its all said and done you'll end up with 40S&W brass but with large primers because 10mm uses LP and not SP primers so you'll have to develop your loads from nothing as there will be no published data for 40S&W brass with LPP.

    As I get older I realize that its easier when you dont try to reinvent the wheel but if its something that you are dying to try and have time to play with then more power to you. I wont stop you. I'm actually curious how that works out.
    I think this pretty well covers it.

    It sounds like no one does it. It looks like a lot of work to make a case thats readily available. I see 2 potential problems with this. The case walls possibly being too thick and working up a load with large primers.

    But it will be interesting to see your results

  16. #16
    Boolit Buddy
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    why??

  17. #17
    Boolit Grand Master
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    Must be a good reason...just not apparent.
    Don Verna


  18. #18
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    I'm still sitting on 40 or 50 lbs of 40 cal brass that I don't reload anymore that will get re-purposed into bullet casings.
    Last edited by 6bg6ga; 01-20-2020 at 10:40 AM.

  19. #19
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    I RSO'd a local pistol range yesterday. I could have walked away from there with a five gallon bucket of .40 S%W brass, I think it's even more common than 9mm brass now. I really should get a .40 if for no other reason.

    I have a 10mm I occasionally shoot, one of the few auto pistols that I really, really like. Wish I could pick up 10mm brass like that.

  20. #20
    Boolit Grand Master

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    Frankly I don't see much problem using LPP in one as I've read numerous posts elsewhere of people using SRP in them with good results. Just lower the starting load and have at it.

    How many on here have experimented with rifle primers in pistols or magnum primers in place of standard? I know I have.
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