Pro-Shot AR Style Bore Guide for 5.56mm/.223 Cal.The AR style Bore Guide with O Ring inserts in place of the bolt carrier group assembly while cleaning to center cleaning rod and prevent chamber or muzzle damage. O Ring seal at breech prevents solvent from entering the upper receiver and trigger mechanism while also keeping chemicals out of the action. Solvent Port makes using CLP Cleaner fast & easy. The AR15 M16 style bore guide can be used for all AR15 M16 M4 platform rifles. Work for 5. 56mm & .