ive shot many 40yard turkeys with 2 3/4" modified and like you i used my duck gun, id suggest if you have screw-in chokes to get a full or extra-full but you should be fine just remember you might ge pellets in the body if you shoot that far away, the best thing i can tell you is let them get to 20-30 yards if you can but i never hesitated takeing the 40+ yard shot, and if your useing hevi's ive shot a turkey at 56yards(measured it) and it stoned the bird