WARNING: FOR DRY FIRE USE ONLY. Attempting to use the BoreRail adapter in live fire training may result in severe injury. The BR4 BoreRail adapters creates a standard 1913 picatinny rail system on specified revolver and pistol calibers. Useful for revolvers and pistols without a built-in rail, or without option to attach an adapter under barrel or under grip. Included in the BR4 kit are four different universal size adapters: 9mm / 357 / 380 - (also works with 38 Sp) 40 cal / 10mm 44 Mag 45 ACP / 45 Colt Apply a very thin coat of oil to the o-rings to greatly improve ease of installation and removal.