Cycling an autoloader is a finely tuned balance of forces. The recoil or gas charge must drive the bolt or slide rearward to extract the empty, carry the empty far enough aft to strike the ejector and eject the empty, and far enough aft to clear the next round coming up from the magazine. The recoil spring must then drive the bolt or slide forward with enough force to strip the new round from the magazine, seat the round in the chamber, and, in locked breech guns, achieve safe lock up. This must be accomplished within the space available without beating the gun to death. Newton’s laws apply- force equals mass times acceleration (F=ma). The force involved in a recoil operated pistol such as the 1911 is a function of the bullet weight, the velocity to which it is accelerated, and how much powder is used. The velocity imparted to the slide is a function of the mass of the slide, the force imparted by the fired round, and the retarding contributions of the recoil spring, the main spring, and friction. Too much slide velocity aft, the result of too little slide mass or too little recoil spring force, can cause impact damage where the slide is stopped by the frame. Too much spring power can actually drive the slide forward so quickly that the magazine spring does not have time to raise the next round into position to be chambered before the slide passes. The result is that a given combination of masses and springs works for a limited range of loads. Varying the mass of the slide is a spendy business, especially in light of the cost and convenience of changing springs.
