I purchased 9mm ammo (9x21mm 123 Grain) from here but it isn't a fit for my S&W M&P 9mm. I'm guessing the '21mm' has something to do with it. I'm also curious about the grain. can someone help to educate me.

Question

I purchased 9mm ammo (9x21mm 123 Grain) from here but it isn't a fit for my S&W M&P 9mm.  I'm guessing the '21mm' has something to do with it. I'm also curious about the grain.   can someone help to educate me.

Trevor D. · Answer

9x21mm is a cartridge designed primarily for use by civilian firearm owners in countries that forbid the use of "military" cartridges which sometimes includes 9x19mm A.K.A. 9mm Luger or 9mm Parabellum. It is very similar but the case will be 2mm too long to chamber properly in any 9x19mm firearms. Grains are a measure of bullet weight and a grain is approximately 0.065 grams. The most common weights for 9x19mm (the cartridge you need) are 115 and 124.

Randy I. · Answer

what you want is 9x19 also called  9mm Luger, 9mm Parabellum you can also use 9mm NATO which is just a slightly hotter load

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