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WECSOG*: Converting 15 round M&P9 Magazines to 17 rounders

Whenever I buy magazines, I look for bulk deals. For instance, every once in a while, Brownells will have a deal on a 10 pack of PMags (not now but they do regularly enough). And sometimes you can get them for just north of $10 each.

Anyway, I found a deal on another site for some M&P9 magazines. So, I snatched some up. When they got here, I realized they were 15 round magazines:


I was a little bummed. I guess they were made for places outside of America, like New Jersey or Maryland or something. They were the same size as the 17 rounders I’m used to, so I decided to take them apart and see what made them 2 shy of a full load:


Seems they compressed a bunch of extra spring at the end of the spring. I suppose I could just order replacement springs. But I grabbed some wire cutters instead and cut off the unnecessary portion of the spring:


They loaded 17 rounds just fine. I’ll check reliability at the next range trip. I may end up buying those replacement springs anyway.

*Wile E Coyote School of Gunsmithing

16 Responses to “WECSOG*: Converting 15 round M&P9 Magazines to 17 rounders”

  1. wizardpc Says:

    I think Colorado is the one with the 15 round limit.

    And on a related note, the 10 round magazines for the M&P22 are really just the 12 round magazines with an aluminium peg press-fit onto the plastic floorplate. Takes less than 5 seconds to convert them to standard capacity and no tools required.

  2. tincankilla Says:

    this is the trouble that Californians and others go through – how to get reduced capacity mags that are not immediately junk when we move to a free state.

  3. guy Says:

    So, do your newly cut springs have the name number of coils as your regular 17 rounder springs or did you just whack off the compressed portion?

  4. HL Says:

    When did you change your countertops to presswood? Seems like a downgrade from the fine granite you usually display.

  5. SayUncle Says:


    I whacked off the compressed portion. I may regret that. We’ll see.


    That’s my workbench.

  6. Stuart the Viking Says:

    I still have a 9mm that SHOULD have 15rd magazines, but came with 10rd mags because stupid AWB. I checked, no chance of converting them.

    So far, I’ve ordered a couple “standard capacity” mags online, but they were all aftermarket and ran like dookie. So it’s a choice of 10 for sure, or 15 (or 17) probably… or maybe… Or, go to the source and pay out the nose for standard cap mags from the gun manufacturer (which isn’t too attractive for a gun that I don’t really use very often).

  7. HL Says:

    It’s just that I have never seen a workbench that doesn’t have the wife’s laundry baskets all over it.

  8. Fred Says:

    I pray dat rascal Road Runner don’t gitch ‘ya. Does a replacement spring still end up cost effective over all?

  9. Alien Says:

    I know there are round extending floor plates for Glock mags, anyone make them for M&P mags?

  10. SayUncle Says:

  11. JohnnyIShootStuff Says:

    Where was this 15 round deal. 15 round mags are perfect for IDPA and even better for IDPA in NJ.

  12. SayUncle Says:

    It was here. Now it’s gone.

  13. Ray Says:

    “If its stupid and it works. Then it wasn’t stupid”

  14. Mike Says:

    Don’t forget to drill witness holes for rounds 16 and 17.

  15. TS Says:

    Wait, this solution was simple, cheap, and worked. The Wile E Coyote School of Gunsmithing (sponsored by Acme, Inc.) teaches solutions that are grossly complicated, astronomically expensive, and fail in spectacular ways.

  16. Firehand Says:

    Stuart, what pistol? I’ve run across several places with all kinds of mags, maybe they’d have one

Remember, I do this to entertain me, not you.

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