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 AR15/M16/M4 family of rifles. Will work for both 5.56mm and .223 Cal. variants. Pro-Shot's 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.