Actually a 6.5 Carcano round loaded with the right bullet might be good.
My driver’s ed teacher ordered a Carcano and was telling us that the darned thing shot right through a pine stump. It had a similar bullet to the early 6.5 Swede loading, just not quite as powerful.
In true army fashion, they will approve the new, improved, 5.57 round bc 5.57 is better than 5.56 and then they will build a whole new gun around it bc nothing curently exists. 20 years from now they will cease development due to budget cuts and cost over runs and announce the return of the 5.56. Yay.
No doubt the creedmore and grendel are fairly decent rounds. To be really effective I don’t you’d want do go below .264. You need a round that is capable of housing a tungsten penetrator, tracer capable with a velocity of no less than 2800 fps bullet weight needs to be a function of desired ballistic coefficient of your standard ball round. I expect such a round could be developed with a respectable weight savings over the 7.62 NATO. If staying with an AR type platform you might want to optimizer the receiver for such a .264 round and developing a really effective compensator as the recoil is going to be significantly higher than the 5.56. I maintain the 2800 fps should be the minimum in the standard rifle length barrel. That way re carbine length barrel would still offer respectable velocity. Just saying...
They’re a great round, excellent coefficient. That basically means they buck the wind much better and fly a lot nicer.