This auction is for a ATI Omni Hybrid AR-15 Polymer Complete Lower with Collapsible Stock Black model ATIGLOW201. ATI’s Omni lower receiver is as strong as aluminum and will accept any .223 caliber upper and magazine. The Omni is a multi-caliber AR15 lower made of reinforced polymer. It is designed after a mil-spec lower and is complete with a lower parts kits, grip and M4 adjustable stock. Made with a high-grade durable polymer material, the Omni can withstand harsh environments as well as everyday wear and tear. Specifications and Features: ATI Omni Hybrid AR-15 Complete Lower Receiver ATIGLOW201 Lower parts kit installed Receiver extension tube and buttstock installed Multi-caliber lower Hybrid polymer with metal inserts Black Note: This receiver has been tested and reliably functions with .22LR & 5.56mm NATO but my not work with higher caliber conversions.