Those are dust covers and will not protect the feed lips.
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Reposted, see below.
FWIW, I keep all my magazines loaded. I do not leave one or 2 out as this was a problem solved many years ago my the manufacturers (if I recall correctly). I even keep rounds in all my rifles so I can grab ANY of them in a pinch.
My understanding is that the constant unloading and reloading of mags is what causes the wear and tear on the springs and followers.
Don’t shoot the messenger….
http://img.photobucket.com/albums/v4...agSpringII.jpg
I keep some magazines loaded.
I recently found a WWII 1911 mag that I loaded in 1974. It worked fine when I fired the rounds from it.
Poor quality magazines like Triple K and Promag and unknown makes, I wouldn't trust at all.
As long as you have good quality springs they don't fatique under constant load. I keep some replacement springs around just in case.
Some aftermarket springs are too strong (Wolff 11 lb 1911 springs) and will spread feed lips. Aluminum mags can also have this problem as previously mentioned.
Wish I hadn't lost all my mags and AR's in that tragic boating accident earlier this summer. Probably didn't help that all of the mags were loaded, thus adding weight... sigh.. they sank soooooo quickly [Rant1]