Re: .510 Whisper dies?
Contact SSK industries for more info. They came up with the Whisper line and may already have dies made.
Best bet will be RCBS (phone, their site has no info). Lee will make collet neck sizer die and seater for $50. Hornady might make a die that big for $90.
My understanding is the 510 Whisper is based on the 378 Wby case shortened.