the only c-mags i have are for the 7.62x39. they run like clockwork. going to order some more of the high priced bastards.
all my 5.56 stuff is bushmaster,colt, D&H, and the plastic p-mags. i even put p-mag followers in all my metal mags. even put some in some old-old aluminum beer can imported "junk" mags and they now seem reliable. i think C-products has a updated follower in their mags too.