Alternative to 6.5 Grendel?

[stanc]

So, we can start with the M-1 Carbine, and then work our way up in case size until an interesting velocity is reached.

For this purpose, I would define "interesting" as the velocity needed to punch through hard body armor at practical engagement distances. Might it be more efficient to determine that first, before spending a bunch of time and $$$ evaluating different cartridges?

Are there any suitable COTS bullets available? I used to have a half dozen of the 7.62 SLAP sabots and tungsten projectiles, but a helluva lot more would be needed to do load development and testing.