You can rifle a barrel in your garage. Search youtube, there are DIY videos.
Btw, you need a rifled barrel to make accurate shots at long-ish distances. For close quarter combat a submachine gun with a smooth bore would do quite well. Something similar to this: https://en.wikipedia.org/wiki/Borz. Any machine shop can crank those out in numbers.
Btw, you need a rifled barrel to make accurate shots at long-ish distances. For close quarter combat a submachine gun with a smooth bore would do quite well. Something similar to this: https://en.wikipedia.org/wiki/Borz. Any machine shop can crank those out in numbers.