Being lazy, simple minded and cheap I went as simply as I could. Same as you, lots of well-safetied wall space, secure from prying eyes. Basically, I used 1x2 strips screwed vertically to the wall, on line with the studs, so 16 inches apart. I drilled 5/16th inch holes at a slight angle, 5 1/2 inches apart and glued in 1/16 dowels, about 5 inches long. This allows full exposure, with the bolt handle side facing out. Also leaves room for a matching bayonet, clip, etc. to be hung underneath. Also used refrigerator-magnet stock glued to the wall, to allow a matching magnet with the pertinent info on it, to be attached and readily removed when rearranging stuff.
These are my principal display items, like the primary battle rifles for each major country. Secondary weapons and countries are kept in A-frame vertical racks.
I would post a few pics to show all, but I don’t seem to be able to find a button to push, so I’ll post this as -is and send the pics separately. Hopefully.