freguency of changing magazines

Question
How often should I rotate magazines for my semi-autos??I generally keep a loaded magzine in the firearm and a loaded extra mag ready.?I'm concerned about keeping the mag fully loade for too long a period and weakening the mag spring.

Answer
This would depend how new or old the mags are, newer mags have better springs to prevent memory, older springs tend to compress more.  You can take mags a part and re-stretch the spring every six months or so.  You can also leave the mag a round or two short so it won't compress so much.