MGW carries a wide variety of Sig Sauer upper receivers for the M400, SIG516, & AR-15 platform of rifles and pistols. Find conversion kits, stripped uppers, and upper / lower sets to build your firearm around. These quality uppers available in .223 Rem, 5.56x45mm, and .300 Blackout provides you with proven Sig Sauer performance and are reliable solutions for your next build or upgrade project. Find several colors to fit the aesthetics of your firearm and get your rifle or pistol firing reliably shot after shot.