A .45 silencer would work, but not well for alternate calibers, unless you had it custom made with internals that were fitted to all calibers. The .45 silencer would just be a very expensive flash suppressor when used with smaller calibers.
The only time you could get the multi-caliber components without spending $200 for each extra part -- which, in the ATF's eyes, are of themselves a silencer. Even the lowly rubber wipe was a silencer at one point. That is why you cannot buy spare parts for an existing silencer. You used to be able to get every part of a silencer from a shopping list -- even the can itself. I know it is a mess, but the government is like that when they think the citizens are arming themselves for revolution (don't get me started on that one!).
You can get halfway decent results using a .40 S&W silencer with a 9MM round, however without the benefit of a tight bore, you will be spitting bullets in a very large pattern. And you will have to get some 9MM sized wipes to seal the chambers, otherwise it will be much noisier.
One approach I have been considering is to build a silencer platform using a .510 caliber baseline. That way, I could use it for my .510 Whisper, .50 PeaceKeeper and for smaller calibers -- the method of which will be a patented approach requiring no additional parts, however, there will be some internal moving parts that adjust the caliber, and I am still considering an additional feature that involves moving parts with each round fired, but that one is a long shot (no pun intended) at best. That idea would be better-suited to a system approach where the silencer is integrated with the firearm action.
So far, I have registered a few names in anticipation of applying for a patent, but if you guys want to contribute some brain power to the next great thing in firearms technology, let fly!
For manufacturers, start with:
http://www.gem-tech.com/product.html
http://www.awcsystech.com/gun_silence.htm
http://www.knightsarmament.com/
http://www.subguns.com/products/cans/
http://soundtechsilencers.com/
http://www.tac-ord.com/products_suppressors.htm
http://www.tacticalinc.com/
