[Joe Brower]

Black Hills ammo, who is currently filling an order for something like 11 million rounds of the new 77-grain 5.56mm, lists the muzzle velocity at around 2,750. By comparison, the 62-grain SS 109 is 2,875 or thereabouts. It would appear that the heavier bullet goes a bit slower, which makes sense. Of course, muzzle velocity could be increased by using different powders and whatnot, but then one has to contend with shorter lifespan for the mechanical workings of the weapon, higher rates of barrel and throat erosion, and shorter maintenence cycles.

[xzins]

See Travis McGee's #56 The new 62 grain ammo has greater accuracy at long range, and penetrates armor etc better, but it is much less lethal than the old 55 grain ammo. The new ammo often drills neat "knitting needle" wounds which may be lethal later, but are not manstoppers now. The old 55 grain stuff was unstable and "tumbled" when strking an enemy, leaving awesome wound channels for much better instant stopping.

62 gr. is too fast and simply punches holes. 55 gr would be even faster, but is more lethal because it's unstable and tumbles on striking the target (because it's lighter?). 77 gr is slower and gives greater knockdown.

Interesting lethality chart. As you increase weight you seem to temporarily decreased lethality. I wonder if the 55 or the 77 is more lethal.