Pro-Shot 'The Stopper' Adjustable Bore Guide 22 to 30 Cali Aluminum with Delrin Tip (BG22-30)Feedback: This will NOT fit Ruger Precision Gen 3 308 Bore guides should be used when cleaning a bolt action rifle. Bore guides protect the bore throat and keep cleaning solvent from entering the trigger mechanism. Pro Shot bore guides are made from aircraft grade anodized aluminum. The bore guide tips and ends are manufactured using the chemical resistant Delrin. The anodized aluminum sleeve holds the brass pin and will not work loose like other bore