I think it's the surefire supressor that can be opened and cleaned, or is self cleaning. I don't remember wich one is wich.
And they make supressor for .50 cal HMG.
A nice thing about .50cal sniper rifles, is that at 1000m and beyond, the round is subsonic, so the target does not hear the crack of the bullet comming in. So if you miss, you have more chances to re-engage. Even if the bullet is sub sonic, it can still rip you appart on impact.
BTW, I'm about to finish a book called Trigger Men.
Very good read on many sniper engagements. Some redundant information, but for the casual reader, it will be new and interesting.