Browning .40 with a Bar-Sto barrel and Accu-Rails. Put 20 rounds of 155 gr. Federal Hy-Shok (not Hydra-Shok) into 1 3/8" at 25 Yds out of a Ransom rest with 2 first shot fliers not counted (they opened it up another 1/2").
That would be my Glock 21, fitted out with a threaded, compensated, Accu-Match barrel in .40 Super. I've shot a couple of sub-4", five-shot groups at 100 yds. Tennis balls at 50 yds are a gimme.