Current health issues is only allowing me to only use double or single barrel guns to hunt with. Since it is dove season, I got up to take my regular morning walk/hunt and I grabbed my first gun, a Diamond Arms single shot 410 bore, which was owned by my grandfather whom used it as a snake gun. After successfully not getting anything, I decided to clean my first firearm that I have had for at least 40 years and noticed it can be chambered in 410 bore or 12 M-M.... 12 M-M??

Per this from another site, 12mm is an early designation for .410.

Shotgunworld.com • 12mm bolt action

I had a early 12 ga. single barrel, with a cut down barrel, about 20" or so. Got a new firing pin made for it, and then tried it!!! One shot and wanted no more of it!!! Stock design, and light weight, no fun! Glad you have one in .410, 12mm that you can use with your health issues, and enjoy playing with doves!

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Wherever my mind isn't
Jim

Way back, the .410 was also called the 36 gauge, and boxes were marked that way. Problem is they are not 36 gauge. I have an old Remington wooden shotshell crate marked .410 (36 Ga) (12 m/m)

Actually, if I remember correctly, a .410 bore is actually somewhere between a 67 and 68 gauge. Granted, years ago, it was mistakenly referred to as a "36 gauge," but a true 36 gauge would have a .506-inch bore diameter. Likewise, the 12 mm designation was also incorrect inasmuch as the .410 bore has an actual metric measurement of approximately 10.4 mm.

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Pack light and cinch tight.