If its too loud with a theoben long series silencer then its probably the action that is being noisy not the muzzle.., try serving it.., clean all the ram and bits inside, re assemble it all with a bit of Molly on the outside of the ram & a smear of light engine oil on the ram internals, then pump her back up to about 10.9 11 ftlbs with your fav pellets.., should smooth out & quieten up a treat :-)
Pm me if you need any more details
Atb
Rhys