The 6.8 x 51mm requires a.308 size AR platform. Why didn't they go with something like a 6mm ARC using Sig's stainless steel case head design (2-part case with stainless case head)? That would give you +3000fps with a 105-108 grain high VLD bullet, +2000 fps at 600 yards and a thousand ft-lbs of energy at the same distance. That would be more than 2x the energy of a 75 grain .223 bullet and only 250 ft-lbs less energy than the 6.8 Sig Fury but in a .223 size AR platform and with much lighter ammo. With the Sig Fury, troops will have to carry a very large rifle and heavy ammo for excess killing capability at 600 yards. Don't like the trade-off. Concede the 5.556 NATO is underpowered, but a 6mm ARC with Sig's stainless steel case head and +3000 fps shooting a 105 grain bullet would have been a nice compromise between weight and long-range performance.
My .02 worth.
