Compression springs, be they recoil or magazine, are actually stressed in torsion. The wire twists as the spring compresses. There is a slight amount of bending, too, but in most cases it can be ignored.
The "life" of a spring needs to be clarified - life until fracture, or life until it loses tension (takes a set)? I think in most cases with guns we're talking set, or loss of tension.
The design of a spring depends on the space it has to fit in, the desired deflection, and the desired forces. The constraint is, if stress is too high for the material, the spring will take a set, regardless of processing, and lose tension.
The designer may in some cases be able to obtain a better design using flat wire, which could reduce the maximum stress, and thereby improve its life. A downside is the raw material normally requires a fairly large minimum order, and special tooling is required to make them. The machinery is special as well in the case of oval magazine springs.
I've kicked around ideas for gun springs. There are a few things that may be worth trying some day.
