I've made a few simple and inexpensive wall mount display stands that require little skill, but seem to display well. I just start with a board of choice and work the edges with a router. I like to stain them in a lighter shade so they contrast with the weapon. Then place the weapon where you want it and mark two spots under it where you need the supports. Then hammer in two large nails for the supports and cut the heads off with a hand grinder or Dremmel tool. Once the nail heads are off, I heat the tips near the end with a torch and bend them up slightly on the end keeping most of the nail perpendicular to the board. Finally, I slide black heat-shrink wrap made for covering electrical slices over the nail to protect the stock and heat it so that it covers the whole nail. Once the nail is covered with black heat-shrink it doesn't look like a nail, and it supports the weapons solid.
I've thought of using wooden dowels for support, but the nails are easier and are barely noticeable once the gun is in place. Dowels might work better to add more clearance for those wide drums (?)