[xzins]

Thanks, Joe. Appreciate the info. Wouldn't the 77 grains make it even faster or is there some physics in play here that I'm not recognizing?

[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.