We have 4 test mags that were put in service in August '05 -  2 of ours and 2 HK maritimes. At least once per month (usually more) they are loaded and shot repeatedly and when we are done these 4 get thrown in the back of my truck and stay there. Rain, cold, heat, etc. No special treatment for them and they are all dropped free and generally abused.

Here they are today - 2 on top are our grey Teflon w/MAPUL followers - below are HK's and to the right is an old GI finish mag for comparison (don't have a clue how old it is). After this pic they go back in the truck to be shot again this weekend - they usually look dirtier, but it rained here while we were in Vegas and it washed some of the mud off them... All 5 still function fine.