The main thing is to pattern YOUR gun to see how it shoots. Will a 20 ga kill a turkey at 40 yds.? Absolutely. I have put 18 pellets of #6 hevi-shot in a 3" circle at a measured 40 yds. with a FULL choke. But remember each gun & choke combo is different. Therefore, PATTERN your gun. A 20 ga & a 12 ga pellet at the same velocith hit with the same energy.