Factory Colt complete lower receiver assembly to build a multi-caliber, single serial number modular weapon system. Compatible with all Colt 901 (.308/7.62mm/6.5 Creedmoor) upper receiver assemblies AND mil-spec AR15/M4/M16 upper receivers. Colt's revolutionary lower receiver and bolt carrier design enable the upper receiver group to be easily swapped out for any mil-spec upper receiver chambered in .223/5.56mm, without tools, using the conversion kit (sold separately), in under a minute. All operating controls are ambidextrous, providing you with flexibility and ease of use. Manufactured to truly meet and exceed all Mil Spec standards. 

Link to parts manufacturer