I just installed a Buckmaster 3-9-40 with out any modifying to the hammer at all on my ultra slug 12ga . I used the Leupold PRW all steel med mounts , they fit nice and just enough room so the hammer will clear . Plus them being all steel they shoud hold up to any recoil of a shot gun .
Slackdaddy , were did you get that cheek piece on you 20ga USH?