[mrerick]

Yes - there are people that literally wrote the book on spring technology. It's actually a very precision and moderately complex thing...

This write-up is useful for understanding how our Luger recoil springs are designed and work:

http://springipedia.com/compression-stress-spring.asp

The recoil spring in a Luger is called a compression spring. These springs are actually designed to take a "set" when they are installed in an application (like around the guide rod that holds a Luger recoil spring).

Since they are actually designed to take a set, they get shorter than they were when they were manufactured. Once this "set" is taken, they generally do not change dimension again in their lifetime.

The compression principal of a Luger recoil spring is the same as that of the coil suspension springs that hold up a car body. You don't see these lose power and tension over their lifetime unless they are abused (by constantly carrying too heavy a load).

Over the life of the Luger, the requirements for the recoil spring changed as the ammunition, the receiver geometry and the length of the barrel changed. The strength of ammunition ignition and the length of the barrel contribute to the force that the recoil spring must absorb, both in intensity and in pulse shape. Various small changes in the geometry of the Luger receiver also changed spring requirements.

Marc