Stretching the mag spring back to its original length is the worst thing you can do to it. It will actually induce more stress and fatigue into the spring if you stretch it back. The only way to get rid of the fatigue in the spring is to heat treat it. This will require equipment in the six figure range. If you feel that your springs are getting worn out, it's best to replace the spring. FYI, I got this info from a 1990 issue of Peterson's Handguns magazine. The author, Mike Izumi, is a mechanical engineer who did a study on magazine fatigue (BTW I'm a mechanical engineer too so I know he wasn't BS'ing).
Corbon91
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