I tried using a sling once, thinking, "Gee, why has no one thought of this." and half way through the match I was thinking "Gee, this is why no one does this." It just got in the way and slowed me down, and I really didn't notice a huge gain off-hand. I tend to practice off-hand (weak and strong side) stability, breathing, and trigger control more than anything but maybe shotgun loading.