Good question. The pictured BCM build is really a hybrid of the Army’s SDM-R and Marine SAM-R. I began building it about 15 years ago but finished within the past 3 years in its final configuration with the following specs:
20", 1:8 stainless steel Douglas fluted match barrel finished with three coats of Moly-Resin, match-grade, two-stage KAC trigger, Daniel Defense ultra lightweight free-float forearm rail, Harris bipod, MATech back-up iron sight, BCM bolt carrier group, BCM lower.