The Windam MCS is a complete multi-caliber weapons system allowing for quick changes between barrels, and even magazine wells, to accommodate calibers including 5.56 mm, .300 AAC blackout, 7.62x39 mm, and 9x19 mm Parabellum. The included barrels, with the exception of the 9mm barrel, feature birdcage flash hiders, and milled aluminum gas blocks with a rail top and bayonet lug. With a milled aluminum quad-rail handguard that does not have to be removed for changing barrels, flat top upper receiver with deflector and forward assist. This system allows for changes in caliber without having to remove mounted sights and accessories. The rifle operates in a direct blowback mode while configured for 9 mm without the use of a block. Standard markings on the lower with a checkered grip, and collapsible six-position buttstock. The fitted case includes the following: three extra 16 inch barrels chambered for the following calibers: .300 AAC Blackout, 7.62x39 mm, and 9x19 mm Parabellum; two extra bolt carrier groups for 9 mm and 7.62 conversion; two each, lower magazine conversion wells for 9mm and 7.62 mm; and one each 9 mm and 7.62 mm magazines; and a nylon sling.