I've just realised the key to making really quiet PCP/CO2 airguns....
..and it's pretty obvious really: you need to attack the source of the problem, not the effect.
Having done this on three guns now (a Rapid, a Kral, and a SMK CO2 rile), the effect is very considerable... even the most basic moderator renders them very quiet indeed...
Over to you folks to guess the procedure (no cheating) I'm talking about...
Always looking for any cheap, interesting, knackered "project" guns. But not lathes. I have too many lathes. Thanks, JB.