Originally Posted By plinkr415:
It's not an MT6601, but I believe that member AKSU stated that his factory M16A4 upper bought from Autoweapons(?) has M4 ramps and an M4 barrel extension.
then he got ripped. cause A4 uppers dont have m4 feedramps
they did the same thing to Jcrowl and he sent it back and they gave him a correct upper