I just got my first AR, and since I live in NJ, I bought from a seller on the equipment exchange list of this forum a few 15-round magazines.
While overall they look good and functional, it bothered me that there is a 1/16" gap between the mag fllor and the rear of the mag body. This is due to a loose fit of the floor inside the mag body, which allows the floor to pivot around the retaining pin, and open up at the rear. See picture below, with the gap visible on the mag to the left, and to the right the partially pulled floor inserted in the much larger mag body:
http://i18.photobucket.com/albums/b137/DMala/ARMagFloorFix_1.jpgI contacted the seller who replied that this is normal and occurs also in Bushmaster mags. Whatever it is, it seems to me that it should have been easy to design a better fit of the mag floor, but rather than arguing I came up with a simple fix.
I just inserted a small screw at the top of the rear side of the mag fllor. This screw can be adjusted to achieve the correct width of the mag floor, which avoids its pivoting rearwards. See photo below with the modified mag floor, the small screw I used, and a properly fixed magazine.
http://i18.photobucket.com/albums/b137/DMala/ARMagFloorFix_2.jpg Note that I used a spring-loaded punch to mark the place where I drilled a pilot hole for the screw.
While doing this it is a good opportunity to remove the small plastic and aluminum shavings that I found in the mag, before they get into the action.....
I hope this helps.