The crossbar studs are only long enough to go in to the threaded washer and through the crossbar with the nuts on top.
It is intended to just glue on to the side, you can get longer studs (10-32 thread) and screw them in if you want.
The prop used in the movie looks like it is painted, but everyone seems to be doing different finishes, so just weathering the existing finish should look fine.
Start light with the steel wool, then work with the heavier abrasives slowly, the side that touches the holster should have a little more weathering than the rest.