Yeah your right, found the mag thing on the wiki chart I posted earlier. So any mags you use in the gun must all have US parts. I knew what I said didnt sound right thats why I keep all mags US parts anyways, its not to expensive.
As per an ATF letter located here, magazine parts are not subject to constructive possession. If you need US-made magazine parts in order to reach 10 or fewer imported parts, then you don't have to replace parts on all of your magazines - only the ones which you intend to use with this rifle. The easiest solution is to only own US-made magazines, of course, but this is not always feasible, particularly if no US-made magazines are available for the weapon in question or, for legal reasons, you can't buy domestic full-capacity magazines to replace your old imported magazines.