I thought this was put to rest a while back. Magazines do not lose strength from staying compressed or uncompressed. It is the usage of a spring that weakens it.
Springs will also weaken greatly if a compression spring is stretched. Every case ive ever come across where someone has claimed a spring weakened from sitting compressed was one in which the owner removed the spring and gave both ends a tug to lengthen it back into shape....
Ive got some 45acp 1911 magazines in my collection that were in use by the 25th infantry division during ww2 korea vietnam and everything in between. Many thousands of cycles of compression decompression and many countless months and days of sitting compressed and they all work fine.
Replacing springs is just not needed in magazines that are working fine. Soon as one starts to have issues replace the magazine.
Almost all magazine issues are strictly related to damage neglect or end user abuse. Leaving one in a compressed state is not going to hurt it.
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