Mk18 CQBR upper receiver groups in all three NSWC Crane generations: Mod 0 (10.3" Colt barrel, KAC RIS or RAS handguard, FSP retained), Mod 1 (10.3" Colt barrel, Daniel Defense Mk18 RIS-II 9.55" FDE rail, FSP deleted), and Mod 3 (Colt 11.5" barrel, Geissele MK16 Super Modular Rail, current Navy procurement spec). Both factory uppers and CCC clone-correct custom builds available. These uppers drop onto any mil-spec M4 or AR-15 lower.
Need help choosing — Mod 0 vs Mod 1 vs Mod 3? Read the CCC Mk18 CQBR Reference Guide for the canonical configurations, the Mod 3 vs Daniel Defense Mk18 RIII distinction, and what makes a clone-correct build.