if done properly the beauty is that you can fire factory ammo in it and still get "reasonable" accuracy in a pinch.. say if you found yourself away from home without any handloaded ammo (that had been fireformed)... most of the ackley variations consisted of taking the shoulder of the shell to 40*and moving the mouth to shoulder vertex back .004 inches as well as removing taper from the body, resulting in, you guessed it, more room for gunpowder...