The Belgian 62 grain bullet was adopted as NATO standard, but has proved to be inadequate in 14.5" barreled M-4 carbine. The US is now moving on to even heavier bullets than 68 grains for the M-4 and other M-16 platforms. The 77 grain Mk 262 round is in current production for special forces and squad designated marksmen using the Mk 12 rifle. MK-262 round sole producer has been Black Hills, but due to increased demand of the round for other M-16 platforms, looks like Lake City will now be starting production.
what is so special about this and why should we care?
Now, I made it a point to say I was not trying to be smart toward you in my original reply... But if you make an error, even innocently, don't deflect to another another discussion in order to draw attention away from the original statement. Just say, "Yes, that is what I should have said, and BTW: the U.S. is currently moving toward even heavier rounds like the current rounds with which the military Spec-Ops guys are experimenting in the field. Those heavier rounds are not yet standard issue to all troops." Now that is an accurate statement to which I would have probably said something like "Cool... They're learning lessons from the old boys that have been busting prairie dogs out at 700 yards with the AR platform."
The fact is that there are currently more than 6 various experimental rounds (XM287, XM288, XM777, XM778, XM779, XM780 just to name the ones I can off the top of my head) and then rounds such as the Mk282 (in Mod 0 with the SMK bullet, and Mod 1 with the Nosler or Sierra) that are in use with U.S. Army and U.S.N. Spec-Ops units in the SPR or (in Navy nomenclature) the Mk12. This is basically the same set-up as the Counter-sniper rifles that I have built for law enforcement agencies for years (where agencies were too cheap to let their designated shooter operate with a 700PSS, an H&K PSG1, or an M-21 or M-25, all good 7.62mm long range rifles.) And yes, I used barrels that would properly stabilize bullets in the mid-70 grain range so that they could increase their distance from the target in the hot zone.
The bullet designer boys for the military are continuously designing and testing new rounds... For them it is job security. If they tell the brass that the military is using the best bullet that can be designed, they would be part of the next RIF.