As a rule of thumb, start your muzzle about half to two-thirds of the way along the target's flight path. Hold the muzzle just below the path of the bird, to avoid unnecessary up-and-down barrel movement when mounting. With this kind of head start, the idea of muzzle speed becomes moot. There's no way for the target to outrace your gun, which can cover a huge swath of sky by swinging just a few inches side to side. The moment you see the target, start your swing while raising the gun to your cheek. Ideally, as the gun touches your cheek, you should touch off your shot. This way you'll avoid "riding the bird," which often contributes to missed shots. A compact, smooth move with your barrels is the final piece to slowing down the target, getting a hit, and gaining proficiency in the art of shotgunning.