If the rifle stayed fully assembled, a small lunch sized bag could simply and easily be placed over the exposed muzzle end of the barrel to hide it. That solution would have been much simpler and quicker than disassembling and reassembling the rifle. The small lunch sized bag could have been disposed of anywhere in the TSBD and would not have appeared out of place.
If a small lunch bag could have been disposed of anywhere, then so could a two-foot long bag.