MGM makes one that uses springs which are more consistent than the shock type that run slow in the morning and snap shut after the sun hits them for a while. All of them can be affected by the wind so not much can be done there. Target and stick weight can alter the speed. You can't just staple a new target on top of an old since it would change the speed of the action. With a little thought they can be made fairly consistent. They are fun to shoot.