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Thread: Ream/bore my cohaire mp5/40 to 10mm?

  1. #1
    Gets the Shakes if No HK Contact in 24 Hour Period
    fullmann's Avatar
    Join Date : Jan 2006
    Location : Big Bay City, MI
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    Default Ream/bore my cohaire mp5/40 to 10mm?

    For some reason, I've been wanting to get into 10mm lately.

    I look at my mp5/40 clone and think it should be a fairly inexpensive update. As a 40 it's been 100% (after a swap to genuine HK BCG).

    So I'll ask any of you that have one or have done the conversion.... Worth it? Or just leave well enough alone?

    If I don't do this one, I'll probably build a DI 10mm AR.

  2. #2
    Desperately Needs Treatment
    SWolff's Avatar
    Join Date : Sep 2009
    Location : PA
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    I believe Jayson @ IGF can ream it. I just don't know if the barrel has to be removed from the gun or if he can do it with everything installed.

    You can also see if Mike @ Michaels Machines has any of his CHF 10mm barrels still available. Probably the best non german made 10mm MP5 barrel. BMP may some SS ones available as well.

  3. #3
    H&K Certified Armorer
    Chopstix Kid's Avatar
    Join Date : Nov 2007
    Location : Michigan
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    Default carries the MM 10mm barrels now.
    Dakota Tactical (07/C2)
    H&K Certified Armorer
    Roller Locks Made Right(TM)

    War does not determine who is right - only who is left. ~ Bertrand Russell

  4. #4
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    whodge1327's Avatar
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    Quote Originally Posted by Chopstix Kid View Post carries the MM 10mm barrels now.
    I bet it would be much more cost effective to ream the existing barrel.
    P7 x 3 (For my three sons)
    MP5 (Ghillie Build)

  5. #5
    H&K Certified Armorer
    Chopstix Kid's Avatar
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    Location : Michigan
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    Quote Originally Posted by whodge1327 View Post
    I bet it would be much more cost effective to ream the existing barrel.
    Likely cheaper, yes. Cost effectiveness is relative...

    Labor to R/R a barel aside, the MM 10mm barrel is what, $350 I think? Most gunsmiths I know charge between $75 and $125 to re-chamber a barrel. Roller-lock chambers are not exactly SAMMI spec so you really should make sure it's someone who knows the HK chamber spec for a 10mm barrel. Plus you have to consider the cost for chamber fluting. Taking a guess here, but I'd say you might be in for a $200-$250 bill.

    Not saying that it would be done wrong, but I personally would rather have the new barrel for maybe $100-$150 more and forego any possiblity of problems. Just my 2-cents.

  6. #6
    Unrepentant HKHolic

    Join Date : Jun 2003
    Location : Las Vegas, NV
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    My limited understanding is the Jason at IGF simply reams the chamber but does not extent the flutes. As with Todd's original roller locked guns, fluted chambers for roller locked pistol calibers are not required for function. Flutes are required for the higher pressures of rifle calibers, but not necessarily pistol calibers. I have not seen a post were someone had gone from .40 S&W to 10mm and as part of the process the fluting was extended. I could be wrong, but I just don't remember seeing anyone post that. It would be an extra PITA as extending existing flutes would require indexing the barrel. So if you want flutes, I'd get a 10mm barrel.

    Personally, I'd think you'd be better off just buying a 10mm clone or barreled receiver at a good price. Shoot it and if you like it, keep it. If don't like it, sell it for what you paid for it. As far as market value, if you spend all this money on converting your .40 S&W to 10mm and don't like it, how much will it cost to put it back to .40 S&W? Certainly, it will be more money up front to buy a 10mm clone, but it would give you more options IMHO. Good luck with your 10mm project.


  7. #7
    Very Senior Member
    ta8218's Avatar
    Join Date : Feb 2013
    Location : St. Louis, MO
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    Just get a 10mm barrel and have it swapped out. It might cost you a little bit more, but then you'll still have your .40 barrel. Sell and recoup some costs, or hang on to it in case you ever want to go back to .40.

    OR.. just build the AR in 10. Then you get to have another gun. More guns=more fun.
    "An armed society is a polite society."

  8. #8

    Join Date : Aug 2006
    Age : 49
    Posts : 68


    Jason converted a MP5/ 40 German kit to a 10 mm works without a hiccup on SW receiver not one FTE....
    usp 9
    tactical .45
    sp 89
    hk 91
    hk 51

    Ant to many other types to list......I have a problem

  9. #9
    Grand Chazzar
    FRANK's Avatar
    Join Date : Aug 2008
    Posts : 3,333


    Isn't the HK chamber spec for 10mm .....10mm ?
    I have several "pistol" caliber roller lock firearms lacking what I consider adequate chamber flutes
    But have never had an issue with extraction..
    Interesting thread....
    As I have a 40 and a 10k would like to make em both 10 .......
    I may contact cotter see what he has to say .

  10. #10
    H&K Certified Armorer
    Chopstix Kid's Avatar
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    As it was explained to me in Armorer's training, the flutes assist with extraction. The orginal MP5 barrels had 12 flutes. Beginning with the Navy model, the number was increased to 16 to better assist with extraction in harsh operating conditions; such as debris in the gun be-it from the environment or from exdended use without cleaning. Obviously at some point in testing it was found that 12-flutes were not adequate. There are likely other reasons, however this is how it was explained to me.

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