.40 S & W
Have a Taurus 99AF (9mm) and a 101AF (.40 S & W)...identical except for the barrel. Going into this "test" I was biased in favor of the 9mm... Setting up steel cans at 50' I fired ten shots with each pistol. I hit the can more often with the .40. The .40 worked as it should an no fouling..I used cast bullets in both. Also ejected cases all ejected to the same area...very nice and easy to find and retreive. The 9mm? Hmmmm...cases ejected all over the place and many too close to my face. The barrel was horribly fouled (yes, I used hard cast bullets, good lube, & they were NOT undersized for the barrel). The fouling was pretty easy to remove with a few passes with a jag tip & a right cotton patch. Despite the fact that I shoot the 9mm much more often, it was not as accurate as the .40. IMHO the .40 is the better of the two calibers.