Quoted:
how do you guys like the acog on the 12.5? how far out are can you hit accurately with that barrel length?
I like the 11 series ACOG so much that I ordered another one for the 12.5" 6.8. It gives up a little speed versus a red dot at <50y, but is much better at ranges beyond that. As mine is not a social platform, I am willing to accept that trade off for my typical applications; besides, I also have a T-1 for the weapon should I choose to use it for CQB-type stuff. The 11's are amazingly bright and "forgiving" with the large EP, and the longer ER also makes BAC easier to implement for me versus a 31.
As MagazineFed alluded to, barrel quality has more to do with precision shooting than barrel length, and ammo quality trumps both of them IMHO. There is a caveat though; reduced barrel length means reduced MV, all else being equal. While this is essentially inconsequential from an elevation perspective, since the operator is DOPE'ing at longer distances anyway, there is more windage influence at lower velocity for a given BC. I am starting to digress into off topic external ballistics discussion, and will stop here.
Regarding your specific inquiry, hitting 8" steels at 300y prone with my setup is pretty easy, even using XM193. I have also shot 18"x30" steel silhouettes out to just under 500y, and it is even easier.... do the math. I haven't tried shooting for groups with better ammo yet, but it is on the agenda, along with several other test programs. This damn thing called gainful employment just seems to keep getting in the way. The N4 seems to be a pretty good barrel, and hopefully I can also run my wife's 16" version some more in the near term as well.
The gist of it is:
1) Start with quality ammo
2) Add a quality barrel
3) Quality optics sure don't hurt
4) 1-3 will probably be capable of better precision than most shooters.
Hope this helps.