Alternative to 6.5 Grendel?

[JASmith]

The E. Arthur Brown Company (eabco.com) sells sabots for .224 bullets in 30 cal cartridges. They also have loading info.
http://eabco.com/Reports/report04.html

So, we can start with the M-1 Carbine, and then work our way up in case size until an interesting velocity is reached. Off the top of my head, the Whisper may be very interesting if one can't get enough from the straight-wall carbine case.