MTM Bore Guide The Bore Guide assures perfect alignment of a cleaning rod to the bore, prevents solvent contamination of magazine and trigger mechanism, and protects a rifle’s finish. If you’re serious about cleaning your rifles these are a must! BGR Small will fit: .17 to .243(6MM) calibers. Fits Remington 700, 788, 40X short actions; Mauser 300, Ruger 77 short actions; and similar bolt sizes. BGW Large will fit: 25 to .378 WBY. Mag. calibers. Fits Remington 700, 788 long actions; Winchester 70 & 54 long actions; Ruger 77 long actions; Mauser 300; Weatherby Mark V long actions & Vanguard actions; Browning A-bolt long action standard & magnum calibers; Savage 110; Mossberg 3500; Sako long actions(AV); and other long actions.