There's a minimum striking force needed to reliably set off the primer. I bet the auto is closer to that minimum. The auto with the softer spring will likely have a longer lock time as well.

If both were of the same striking force, yet each different in spring force, the amount of travel and moment of inertia of the hammer would have to make up the difference in spring force.

Last edited by Chuck H; 11/15/15 09:37 AM.