We've had this discussion before -- and, except for the M855 experience, I do not have data to suggest a more optimistic ballistic coefficient than you suggest. So, incorporating the "more mundane" ballistic coefficients is why the "Battle Rifle Cartridge" study listed above suggests that the Grendel is a little shy of being good enough by the standards of that discussion. The "6.5 mm and the Politics of Procurement" discussion uses the Scenar and and is looking at a full-length cartridge, so the service that adopts it would need to do a more-or-less complete replacement of infantry firearms. These folks are somewhat more optimistic with their views on realizable ballistic coefficients and their consensus is that a BC of about .52 might be attainable in a production 8 gram (123 grain) bullet. BTW, it looks like one would need 40-44 grains water capacity to get the desired 800 meter/second muzzle velocity in a 20" barrel.