Yes, it can be legal to make a silencer. For everything Form-1, from silencer designs that are easily made, to filing forms with the BATF, to 3D modeling. Remember, you must have an approved BATF Form-1 to make a silencer. All NFA laws apply.
Cannot find any information on if the Torrent QD mount is a parented design or if it’s public. I know the name is copyrighted, but don’t see anything on the actual design.