Alternative to 6.5 Grendel?

[Variable]

Very true. There are of course already SLAP rounds with tungsten penetrators developed in 7.62x51 - one version has seen Swedish service in sniper rifles - and I even have a saboted 5.56mm round in my collection (although I have no idea how effective it would be!).

There might be some implications for rifling twist selection, I'm not sure.

Any accuracy info on the sabo sniper ammo? Not saying it couldn't somehow be made accurate, but my past experience was very poor.