CapnMac
Member
Given that program, a spitball:Fire protection = no
Break in/theft resistance = yes
Esthetic = no, just needs to be hidden
Water resistance = no
Humidity/temp control = yes
Choose an under-used closet of a suitable dimension. Clear all the stuff out of the closet. Measure and mark out the stud locations on the back wall.
Given that you want a horizontal orientation, while in from of the wall, mark out the highest, vertically, you want to reach up to stow a rifle. Similarly, mark out the lowest elevation while standing.
That space below to the floor can be used to advantage, with shelves for ammo boxes.
So, we can picture a box, with legs and/or sides, and shelves below.
Because of your preferred orientation, this box does not need to be deep, which can be used to advantage. If with a wrinkle.
This box will want to be about 54" wide. The closet is probably not ±12 + 26" deep, so that suggest that you need three doors, with two of those hinged together. How to latch that properly will take some separate brainstorming.
Oh, for a cheap way to line the inside of metal cabinets, one of my bros swears by the playroom floor mats; they come in big bundles at the box store, and the edges mesh together, and are easy to cut around brackets and the like.