Sorry for the necrobump, but figured I'd post my findings, in case someone else wants to know.
For my ASG AW .308 my airsoftguy said he had an adapter that fit. I promptly went there and had him demonstrate that it fit. It did, so I bought it and a silencer.
Now this would be great, however my rifle isn't the same as his showroom one, so the adapter wouldn't go all the way in, meaning bb's got shattered inside the silencer. Luckily, he had the silencer that was supposed to fit the adapter, and after fiddling to get it on (lots of dissassembly), I had a huge silencer, that was short enough from the end of the inner barrel to the edge, letting bb's get out cleanly. The silencer is slid onto the outer barrel, so now it looks like I have a shorter barrel, with a huge silencer on.
Now, for the
tl;dr, the adapter is
Swiss Arms CCW adapter for the SA1. The silencer is a
Cybergun/Swiss Arms G.O.O.B Silencer 320 x 45 CCW. As far as I can tell at least. If you have this rifle, the adapter MIGHT fit properly, allowing all sorts of barrel extensions. Be warned that it might also shatter bb's and make a mess inside your silencer
Lastly, a
crappy cellphone picture of the finished thing ^^