3D seems like a lotta effort for what could be done with a chunk of milled butcher block. I made several tattoo guns years back out of butcher block, and as far as I know they are still going. I still have one somewhere around, haven't seen it is a while. A sabot for a machined bolt would have got my attention more than a plastic printed round. Cut the head off of the bolt mill three slots, and use three straight razor blades for stabilizing would make for a very effective round nestled in a sabot.