I recently built an AR (my first build :)).  It's a 20" stainless free floated A3 upper, A2 stock, and a Rock River lower.  I noticed that when my 30 round mags are loaded with 30 or downloaded to 28 they will not seat fully in the magwell.  I've heard of this problem with fully loaded 30 rounders but thought that downloading them to 28 was suppsed to fix it.  It is possible to seat them all the way but it requires a significant tap.  Is there anything I can adjust to fix this or should I just chalk it up to teething problems?  Thanks guys.

Same thing happened to a squad member in the field. Che the mag catch hole in the mag. Older mags sometimes get smashe and the bump for the hold gets out of whack. If your using surplus mags, I'd try bending the top part of the hole out a little

FWIW.....

Are you using Thermold mags ?

I am using USGI 30 and 20 rounders.  I havn't had a chance yet to try anything but I'll let you know if I get it figured out.