US Patent 10145638 Firearm rotation limiter and method

A method and apparatus for limiting the amount of rotation of a upper assembly in relation to a sub-assembly is disclosed. The apparatus comprises a pin corresponding to a pinhole of a sub-assembly of a firearm. A bumper is coupled to the pin by a connector. When the pin is placed in the pinhole, the bumper will prevent full rotation of the upper in relation to the sub-assembly while allowing some separation. The method comprises replacing a front pin of a firearm with a pin such that bumper abuts the upper and the sub-assembly when the upper is rotated about the pin. When the upper is rotated, the magazine is removed.