Calibers: 5.56 NATO; 7.62x51. Come with LMT Monolithic Rail Platform, MRP upper receivers, mil-spec lower. Lacks ambidextrous controls of MARS system. S-A bolt carrier group, Defender lower receiver. 14.5” Picatinny top rail, M-LOK-compatible attachment points on other rail faces. Low-profile gas block with straight gas tube; textured grip, M4-style stock, and dry-film-lubricant-coated extension tube. Values are for the Defender-L 5.56 16” model; add 32% for the Defender-H 7.62 16” variant.