The issue is that 11.5" 5.56 guns have a pretty significant velocity penalty compared to 14.5" and 16" 5.56, so some things that are true with one are not necessarily true with the other.
Yes, I am a pretty vocal proponent for a 100 yard/meter zero for most things, I am not a staunch enough proceduralist to eschew a 200 yard/meter zero if the optic or application favors it.
There is a whole discussion to be had on exactly what constitutes a "zero", but that's a discussion better left to another thread.
Anyway, one of the reasons that I favor a 100 yard point of aim/point of impact intersection with carbines is that the trajectory "slope" from muzzle to 100 yards is very gradual, and therefore very easy to apply even on fairly small/technical/high importance targets while under significant stress, as long as you have done at least the same amount of work in applying your hold-overs as would have to be invested in a 50 yard zero (or 200, or 36, or 10, or whatever) for the same target size. Basically, it enables me to precisely place projectiles (without thinking about it) into a 3" diameter target from 3 yards to 125 yards, and into a 9" target out to 200. I really don't need to worry about hold-over until past 200.
HOWEVER, the velocity penalty of 11.5 with most ammo makes things a little muddier.
For this example, I'm going to compare a 50 meter, 100 meter, and 200 meter zero with a 62gr projectile at 2650 f/s with a 2.7" line of sight over bore.
The first problem is that with a 100 meter point of aim/point of impact zero, the projectile reaches it's apex at around 90 meters, and the projectile path actually crosses the line of sight (initial point) at around 70 meters, so, rather than the gentle 100 meter slope that I prefer, the slope is actually closer to a 50 meter "zero" with a 16" gun than it is to a 100 meter "zero". There are still some benefits of a more gentle 70 meter initial point trajectory, but it's not quite as profound with regard to distance windows of similar hold-over as with a more speedy launch.
Anyway, when it comes to longer range performance, at 200 meters the 50 meter zero will be about 3" below the point of aim while the 100 meter zero will be about 5" below the point of aim. No significant difference between the two. The 200 meter zero will, naturally, be dead-on the point of aim. The problem with the 200 meter "zero" is that it's actually about a 35 meter initial point in the trajectory, and that early of an initial point means that there is more to think about inside the 3-100 yard application, where 11.5" guns are really the most applicable, and where preserving life has the tightest time budget.
If you go to slower moving, but more terminally effective ammunition, such as 75gr GoldDot, 70gr TSX, or 77gr Mk262, the difference between the 100 meter and 50 meter trajectory slopes narrows even more, and frankly to the point of arguing semantics and personal belief more than actual performance differences. That said, I still prefer to zero POA/POI at 100 yards, because I want to know for sure that inside my most likely engagement distances that will likely have a high precision component to successful resolution that my bullets are going exactly where I expect them to be, and 50 yards doesn't quite give me the confidence that I want for that tool or condition of use.
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Originally Posted by the_1iviper
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