You can make a pistol suppressor from seamless tubing and steel wool, threaded barrels are not uncommon or controlled. You’ll be missing the booster needed for reliability, and it’s not going to be very good, but expansion chamber volume is expansion chamber volume. Reportedly the shooter had more than one malfunction, which lends credence to a DIY can, or a shitty gun.

If the goal is murder, another +15 years for NFA violations isn’t a big deterrent.