The locking gun mounts that are used in police cars can be used in a building. They have both electric and key releases. Google "police supply" for many on-line sources. One catalog that comes to mind is Galls. I use one in my house for my at-ready boom stick near a door. It holds my Remington 760 pump 30-06 which is my hog gun and my big caliber option for a defense gun here at the ranch. The 760 rifle is so similar to the 870 shotgun that the gun rack for a shotgun fits the rifle as long as it is not scoped. They make them for several shotguns and rifles including AR's. When locked, the gun actions cannot be cycled while the gun is in the rack, so it adds a safety factor in that you can keep the gun's magazine loaded with the chamber empty while it is in the gun rack rack. You can also google "police gun rack".
