The Pro-Shot AR style Bore Guide slides in place of the bolt carrier group assembly while cleaning. This centers the cleaning rod while the o-ring end prevents solvent from entering the upper receiver and trigger mechanism during the cleaning process. This bore guide can be used for all of the AR15M16M4 family of rifles. Will work for both 5.56mm and .223 Cal. variants. Pro-Shots bore guides are manufactured with precision quality Delrin and include a solvent port. The bore guide is chemical resistant and will stand up to harsh chemicals, providing continual use.