Also, RRA LAR8's are proprietary. No other brand upper/lower will work with the RRA "AR10" platform. This rifle was originally designed as the Bushmaster BAR10, a 308 AR designed to use FN FAL magazines. I have one of the old BMs, and I must stick with RRA for upper assemblies, bolt carrier groups, etc.
RRA's AR15 platforms WILL accept other brands upper/lower parts.