American Specialty Ammo is selling a registered NFA suppressor for $55 (+ $200 tax stamp) that is nothing more than an adapter to attach a car oil filter to a 1/2-28 threaded barrel. The first bullet punches a hole in the end of the oil filter.
You can buy “spin-on” oil filters for $10 – $20. A used oil filter (soaked with old oil) will only improve its efficiency. Internally oil filters contain fibrous material designed to filter out contaminates from the oil. I think they would eventually wear/burn out when used with firearms.
This is a very clever concept. It makes me wonder why someone doesn’t make a universal suppressor adapter and a range of tubes for various calibers.
Personally, I would rather buy a well-made suppressor rather than risking a oil filter exploding in my face.
[ Many thanks to jdun1911 for emailing me the link. ]