Did RR ever drop the FAL mags?
The LAR-08 still uses metric FAL mags, or the RRA poly equivalent.
The LAR-BT3 uses DPMS pattern - I think, couldn’t find that information specifically called out - other than it’s magazine not compatible with the LAR-08.
The LAR-08 has the Armalite “angle” cut on the receivers, the LAR-BT3 is the radial rounded match up.