I'm reading a lot of opinions about the 16" carbine. I'm having a hard time wrapping my head around a 16" barrel for distance shooting and accuracy. I've been trained to think that the 18 ~ 20 is the better choice for accuracy. Let me define.. dime size groups at 100 yds.
Couple of things...
First and foremost is that barrel length has nothing to do with accuracy, it has to do with velocity of the projectile. Higher velocity projectiles will fly "faster" and "further", thereby also being "flatter", but this will not affect group size and will only affect POI change at various ranges. Velocity will also affect how the bullet performs in soft targets since all bullets have a velocity floor, below which they no longer perform as designed and, when significantly below the floor, start punching 1/4" holes in things and not much else.
Wes Grant, of MSTN, has posted pictures on ar15.com of targets he's shot at distances of 100 yards (and over, IIRC) with Noveske stainless steel barrels in the 7.5" to 10.5" range. The accuracy of these barrels, for those that are used to thinking longer=more accurate, is astounding.
Second, 100 yards is not "distance shooting". We were just shooting at 4" steel plates at 100 yards at our last match and guys with iron-sighted AKs were hitting the plates. No, that's not dime-sized groups, but it's awfully good shooting and it illustrates my point. "Distance shooting", to me, begins at ranges past 200 yards. At 200 yards I can hit a 6" steel plate with XM193 using a 4 MOA Aimpoint. It's also the distance at which I prefer to zero all of my ARs.
Third, if shooting dime size groups at 100 yards, whether it's considered "distance shooting" or not is not the forte of the M4-pattern carbine. Even for a rifle like the Noveske N4 (which is probably capable of damn-near meeting your requirement) the rest of the feature set of the gun isn't what I would consider ideal for that kind of accuracy.
I'm working on putting together a precision AR on a lower that I have coming to me, and it will get a more stable stock than the Noveske and a better trigger, and that's just components in the lower itself.
which again, isn't to say that the Noveske N4 won't meet your accuracy requirement, just that it's probably not best suited to it. Noveske sells other rifles and barrels that would be more appropriate IMHO.
Finally (and this really should have been first), be careful what you wish for. Dime-sized groups at 100 yards are a special skill, forgetting entirely about the gear for a moment. You need to have the skill set to know how to pull that off so that you don't resort to blaming the gear/ammo/gun/wind/guy farting next to you on the line/etc. However, this kind of shooting IS gear specific, and that extends to the ammo as well as the rifle. I see guys at the range all the time shooting Wolf through 24" heavy bull barrel guns with 10x optics and can't for the life of me figure out what it is that they're after.