How does 200g .400 projectile going 2300 fps sound?
(http://img.photobucket.com/albums/v465/CWLONGSHOT/9CC3D143-F8F0-4D83-A729-918885D91260_zpsfs6qbrgk.jpg)
(http://img.photobucket.com/albums/v465/CWLONGSHOT/8F8F6061-EDF0-4C95-99EF-FFF52A4113E4_zpsxiesj396.jpg)
(http://img.photobucket.com/albums/v465/CWLONGSHOT/AB06BA5B-D831-43C0-A167-6B2F7DAA19BA_zpsndopcpaf.jpg) (http://smg.photobucket.com/user/CWLONGSHOT/media/AB06BA5B-D831-43C0-A167-6B2F7DAA19BA_zpsndopcpaf.jpg.html)
As I understand it was developed in 2014.
Being a 10mm guy like you'll. I like the idea!!
CW
I looked at some wildcats like this when contemplating an AR-10 big bore builds. The 45 Raptor was on the short list.
In the end I stuck with the non-wildcat but nearly forgotten 358 Winchester. Very happy I did.
The problem with a .400 wildcat rifle cartridge, at least for my tastes, is the lack of a good sleek heavy with a high BC/low drag. Something like the 408 Chey Tac shoots, but at whisper velocities. That, of course, would require a shorter case than the one for the 400 AR.
OTOH, I am glad to see guys wildcatting 10mm projectiles. 10mm is definitely the best mm.