#html-body [data-pb-style=P5VTP1R]{border-style:none;border-width:1px;border-radius:0;margin:0;padding:0}Genuine replacement barrel for the 5.5" 5.56NATO Rattler. Complete with barrel and gas block assembly.. *Please Note This Barrel is compatible with the Rattler ONLY. This barrel is not compatible with the MCX Virtus or Legacy MCX Uppers. It will not function with a factory .300BLK handguard. This barrel requires the 5.56NATO Rattler handguard. SIG SAUER offers upper assemblies and caliber exchange kits in various barrel lengths. All NFA rules apply to the installation of these upper assemblies to lower receivers and caliber exchange kits to upper receivers. Upper assemblies and caliber exchange kits with barrel lengths less than 16 "may only be affixed to lower receivers that (1) are not recorded as a rifle lower by the manufacturer and do not have a stock attached to the lower receiver or (2) registered with the BATFE as a short-barreled rifle (SBR). Please check with your local and state municipalities for any further regulatory requirements. It is your responsibility as the buyer of these components to make sure you comply with all NFA rules and applicable laws.