Based on my knowledge of Physics I'd tend to agree with 45 Colt's pistol smith's remarks about increased power recoil springs.
Weldonjr2001 is correct in that the bullet recoiling backwards is greater than the force of the spring pulling forward. This is done for reliability reasons: If the spring were more powerful than the recoil from the bullet, the slide might not go back far enough, causing the case to not eject properly, or at all.
One could actually use a 2 lb recoil spring in the gun if the slide weighed enough. The gun might have slow follow-up shots though
The purpose is as stated before only to bring the slide back to its starting position by storing some of the energy created by the cartridge. A gun with a light weight slide, and a strong recoil spring would thus allow for the fastest follow-up shots... a gun like the P7... though the delay caused by the gas system might affect the time a bit I don't think it is a significant increase.
Another effect of the recoil spring... if my Physics are correct here would be to spread out the recoil of the cartidge. Any other Physics Pholks listening correct me if I'm losing it here.
A portion of the recoil is soaked up by the spring, but part of it (the part not eaten by the spring) hits going in the opposite direction of the bullet, hence hitting the front of the frame (where the motion of the slide is stopped when it strikes a piece of the frame). The rest of the recoil... is travelling in the same direction as the bullet is moving, when the slide snaps forward, and strikes the back part of the frame, but in the opposite direction of the previous force. This make sense to anyone else but me?
Oh... wait... hmm... all right whoever is following me I had another thought. When the slide is recoiling the spring is pressing against both the slide, AND the frame, the latter of which is pressing against your hand, creating something of a "slow and steady" recoil, rather than the snap that comes once the spring has stopped eating the recoil. Ahh... OK I'm pretty confident now. Anyway, anyone else wanna run this through their head real fast for me?
-Morgan