I think there are only 5 and 15 round mags, does your mag have a slot down the rear spline ? If so I think they are the ati mags. Sounds like the same hand guards I have, I cut mine off the the slots started. Does your upper have an adjustable gas system ? Not sure if they all do or not. Just before where the slots start in the hand guard, on the top there is a screw with a detent that adjusts the gas on mine.
No visible slot in mags. The back strap is slightly extended.
No gas screw in handgard.......anywhere.
I can see what looks like the bbl nut.......Its round and Knurled...maybe 1/2" f to r.
Magazine is probly a 15 and matchs the Charls Daly design.
Box is brown with No name...no paperwork......Bought it a few years back and all info is gone off GB......In this search I found 3 uppers I'd forgot about..300 bo ,Calico for the M11 ,and an AMP 11.....whoops.