I found a box of 9x21 brass that I had shot thru my P&R Medusa and on a whim I dropped the empty brass into my 986. The 9x21 brass fit the 986's cylinder bore perfectly just like .45 acp fit the M25s and M625s. The cylinder rotated without problem using 9x21 brass in the 7 round moon clips as well as inserted into the cylinder without moon clips.

I have not seen any 9x21 ammo for sale for years but when I shot it out of my Medusa it was less powerful than 9x19 +P and about equal to military 9mm. I would recommend that you NOT shoot 9x21 out of your 986 due to S&W warranty considerations.

Does anyone know why S&W bored the 986 cylinders 9x21 instead of 9x19?

Mark