US Patent 10054378 Firearm and firearm buffer assembly

A black rifle including a receiver with a bolt carrier movably located therein, a receiver extension tube connected to the receiver, the receiver extension tube including an aperture disposed at an end of the receiver extension tube, and a buffer assembly having an interface surface configured to interface with bolt carrier and being configured to reciprocate through the aperture within the receiver extension tube, the buffer assembly including an open fluid passage, through the buffer assembly, that is sized and shaped for enabling movement of the bolt carrier relative to the receiver and effect automatic or semi-automatic fire when the receiver extension is at least partially filled with water.