This (below) is probably the best engineering / chemical/ physics answer, but it assumes that the material used is not deformed by that first initial full load, or x loads after that. Cycle of one over time.
Simple test is to have 50 new springs, measure them all before, and after a full mag load, then tabulate the lengths. Ideally, to do the same test over a few ranges in time
: Immediately, 1 month, 6months, 1yr, 10 yr., etc. to see what effect time has on compression x length of spring.
All I know is I have personally squashed once and shortened many a pen spring in my time.
Originally Posted by gunderwood
I decided to look at custom/high performance spring manufactures (not gun springs). I wanted to look for a generic, engineering answer and I found one.
In short, the engineering community agrees that springs do not have issues with storage in a none rest state as long as the are operated in a range of compression or elongation that does not deform the spring. Instead the consensus was that springs wear out through cycles. Thus, your mag springs get softer or wear out by loading/unloading the mags.
Storing any number of rounds in a mag (0-max) has no impact on spring performance or lifespan since you do not deform the spring (if you did it wouldn't work after the first load/unload cycle). However, changing the follower to cram another round or two into a mag might compress it enough to slightly deform it.