A little quick research. Springs degrade in 2 ways.
Fatigue which is the result of cycling and is usually after 10's of 1000's of cycles. I don't think this is an area of concern for a magazine (more like for valve springs in a car).
And creep/relaxation which occurs from being under continuous load or compression. The amount of relaxation (as applies here) is a function of the load, temperature (not really valid unless your the guy that hides his ammo in the oven ;-) ), and time. So I would think storing a fully loaded clip over a long time would relax the spring. As the load on the spring as it compress is exponential, those last couple of rounds in the magazine will stress the spring the most. 8 to 10 in a 13rd clip would sound like a good choice. I'm happy with my 10 of 15 choice.
Some spring info here: http://www.lesjoforsab.com/technical-information/durability.asp
Incidentally, reducing the rounds would be less stress on deforming the ammo as well. Good point.
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Engineer, Scout Leader, Motor head, Shooting sports enthusiast
Fatigue which is the result of cycling and is usually after 10's of 1000's of cycles. I don't think this is an area of concern for a magazine (more like for valve springs in a car).
And creep/relaxation which occurs from being under continuous load or compression. The amount of relaxation (as applies here) is a function of the load, temperature (not really valid unless your the guy that hides his ammo in the oven ;-) ), and time. So I would think storing a fully loaded clip over a long time would relax the spring. As the load on the spring as it compress is exponential, those last couple of rounds in the magazine will stress the spring the most. 8 to 10 in a 13rd clip would sound like a good choice. I'm happy with my 10 of 15 choice.
Some spring info here: http://www.lesjoforsab.com/technical-information/durability.asp
Incidentally, reducing the rounds would be less stress on deforming the ammo as well. Good point.
__________________________________________
Engineer, Scout Leader, Motor head, Shooting sports enthusiast