As said before, a silencer is a firearm as defined by the feds. Obtaining ATF authorization to make or buy one is a routine matter and never denied as long as the forms are filled out correctly.
As long as the silencer is registered, you maintain control of it at all times (you are with it or it is locked up with the only key with you) and do not commit a crime with it, then the ATF does not care what you do with it or what firearm you use it on. Some people buy a 30 caliber silencer and use it on everything from 30 caliber on down. I made my 30 caliber silencers with a bore large enough to use on my 338 caliber rifles also.
There are some restrictions on repairs and replacement of parts though. An unlicensed owner or builder can not make replacement parts (except for wipes), make the bore larger or make repairs that result in a longer tube unless they pay another $200 tax. A licensed class 2 manufacturer can replace internal parts, but not the tube or make the tube longer. The class 2 can replace the entire unit if it is one they originally made.
These restrictions mean that manufactured silencers are made to last, this is why they are expensive. A good silencer will last years and thousands of rounds as long as it is not overheated or mounted out of alignment with the bore. Baffle strikes can blow the silencer to pieces at worst, or merely cause inaccuracy at best.
Silencers made with rubber wipes will last 50 rounds or less. But wipes can be replaced as long as the originals are destroyed first. I do not know of anyone who still makes silencers with wipes.
Good sites for info on silencers is
http://www.subguns.com and
http://www.silencertalk.com . You can find links to manufacturers at
http://www.silencertests.com/links.htm .
Ranb