Lets start over: how do you design a GPC?

[mongoosesnipe]

That all depends on how you define performance if you want a cartridge capable of killing effectively at 1k the Grendel can do it on paper it still has the muzzle energy of a 357 mag at 1k. Now if the question is to make a smaller cartridge that can match the muzzle energy of a 7.62 nato while maintaining down range performance the answer is simple, no not practicaly I mean you could have something like a 6.5x47mm the case I 4mm shorter though the overall cartridge case length is near as doesnt mater the same my point being with some of the newer high performance powders and strong brass you could bump the pressure up a little to match 7.62 NATO with a smaller case but the case wouldn't e so much smaller as to fit into say a ar15 chassis but maybe not need an ar10 but then there is that dirty L word that keeps things the same so long as the system is functioning in its current state