Have a try with H&N FTT's as well, Weihrauch have tested them in the HW100 and say they are OK! Be also aware that Hull Cartridge Company have set-up ALL HW100's at 11.5 ft.lbs using RWS Super Domes, in .177 & .22, so IF you use a heavier pellet such as Magnums, the power goes OVER 12 ft.lbs.
Also you can either buy a slip on Silencer, from Target Sports of Bolton, or you can ask then to have their Engineer, Dave Mercer, screw cut the barrel to 1/2 UNF and fit his own superbly QUITE silencer. I had mine done last year and the silencer's the best I've ever used.
Saddle Tramp.