Firearms; firearm attachments, namely, mounts for attaching gun sights to a firearm, mounts for attaching accessories to a firearm, modular external rail system for attaching accessories to a firearm, mounts for attaching ancillary equipment to a firearm, mounts for attaching telescopic sights to a firearm, mounts for attaching lights to a firearm; mounts for attaching smart phones to a firearm, mounts for attaching grips to a firearm; mounts for attaching laser pointing devices to a firearm; mounts for attaching night vision devices to a firearm, mounts for attaching bipods and stands to a firearm; firearm hand guards; non-optical and non-telescopic gun sights; mountable Angle Cosine Indicators for a firearm; swivels for attaching accessories to a firearm