New Cartridge Developments and Implications for Dismounted Infantry Soldiers

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So we still need eco-friendly?

I reckon so. I haven't seen any sign of the need being dropped.

I agree, its tougher to do, but its still doable. In fact, a solid copper bullet would work. 180 grain Barnes with a BC or .473 can be loaded easily to 2700 FPS with easily available powders. Using the newer Superperformance powders, I'd bet you could get over 2800 out of them, at standard length.

I doubt that solid copper is a viable option. For one thing, it probably would lack hard target penetration, judging by your photo of the Barnes 6.5mm 110gr solid fail to penetrate (3/8"?) mild steel plate.

Would probably need a "stretched" M80A1. The attached pic shows 149gr, 165gr and 200gr versions. If I'm not mistaken, the very long bearing surface would negatively impact muzzle velocity and barrel wear.

Going by the increased penetration claimed for 5.56mm M855A1, the 149gr M80A1 ought to give substantial improvement, perhaps comparable to a heavier version at slower MV.