Decided to see if I could 3D print a moderator for my non-FAC air-rifle because it was raining and I enjoy the CAD work:
It's smaller than a SAK and cost just over £1 to make, took about 6 hours to print in one piece. Because of the plastic I was using to print it with, it looks a little bit like something you'd buy from Ann Summers:
The threads were chased out with a tap and it fitted onto the rifle very easily. Seems pretty effective but not sure whether it's as good as a commercial product. My non-scientific pressure tests did indicate that it would cope with a muzzle blast higher than that of an air rifle but I don't think it would be wise (let alone legal) to attach this onto a firearm, unless you have it listed on your ticket.