New Cartridge Developments and Implications for Dismounted Infantry Soldiers

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Why? It can be penetrated fairly easily with the right velocity and projectile. My 7mm WSM blows through steel plate that AP 308 barely penetrates.

If you meant that making a 6/6.5mm bullet from a carbine do it, I understand. None of the Grendel loads I tried made it through, Including AP 130 grain loads, though I haven't tried the 110 grain AP loads yet. I think velocity has a big part to play in AP penetration.

Certainly, if you get the velocity high enough, as with your 7mm WSM, you could no doubt defeat hard armor with ordinary bullets. But this thread -- and Tony's -- is about service ammo, fired in 14.5-20" barrels, most likely at less than magnum velocities. Neither 5.56mm M855/M855A1 Ball nor 7.62mm M80 Ball will defeat hard armor, and I still think it most improbable that the hypothetical 6/6.5/6.8/7mm service ball cartridge will do any better.