Quote Originally Posted by Muddydawg75 View Post
I'm not sure, .510 whisper is 750gr and flies about the same as a 45auto...

I'm very interested, and really want to know more about your project. PLEASE keep reporting back what you find, and if I come across anything I'll post up here as well.
Looks like 510 Whisper is intentionally loaded down to sub sonic and can be loaded quite a bit hotter if desired.