RE: Thermold Mags for AR-15
I have 2 of these mags and have no trouble with them at all in a regular AR-15.
What might be the case though if the notch for the mag catch is too low on the mag it may cause it to ride higher in the AR' s mag well enough for the bolt carrier to drag across it some when cycling.
Also the feed lips are on the thick side and maybe touching the bolt lugs as well.
I' d suggest manually operating the action with an empty magazine and see if you notice the bolt carrier assembly rubbing on these magazines.
I have a Carbon-15 as well as a regular Colt 6400c carbine, due to the wider and rounded bolt lugs on the Carbon-15 and the thicker feed lips on the mags they won' t work in it, while in the Colt they work fine.