My twist is 1/9...will that make a difference from what is on that chart?
Looks like the bottom line is a 25 yard zero. Well, I can do that easily enough, at an indoor range. Thanks!
Buy a magnifying optic.
So it's a 20" barrel? I'm assuming it has a 8/3 rear sight?
IMO, for 99% of shooters there's not enough difference in trajectory between a 20" barrel and a 14.5" or 16" to notice, but the 8/3 sight vs. 6/3 sight does make some difference.
Don't mean to insult anyone if this is common knowledge to users here, but on a M16 sight, "from the factory," the sight is generally designed to be bottomed out at the 8/3 mark (or 6/3 for M4's and many or most commercial AR15 sights). Then your original military zero was for 300 meters, and here my memory is a little fuzzy, but I believe the first crossover for that is around 36 yards. Meaning if you bottom out your sight at the 8/3 or 6/3, then zero at 36 yards or so, your 8/3 or 6/3 mark is zero'd for 300 meters, the 4 mark is zero'd for 400 meters, 5 for 500, then on a 6/3 sight you come back around to the 6/3 top'd out and are zero'd for 600 meters, on a 8/3 you get a 7 mark for 700 and top out at 8/3 for 800 meters.
Then you have Santose come up with resetting the rear sight drum to bottom out 2 clicks lower than the 8/3, or IIRC 4 clicks lower than the 6/3. What this does is allow the shooter to zero that new bottomed out click at 50 yards, which gives a 200 meter zero and has alot of practical benefits since you have a point of impact with 2.5" or so of point of aim from 0 to 250 yards. Then the sight is raised from the new bottom'd out spot to the 8/3 or 6/3 which is still a good 300 meter zero, the 4 is still a 400, etc.
This was originally used with 55gr M193 ammo, and therefore the same trajectory doesn't apply exactly for other rounds which has to be considered if you use different bullet weight than that. Also note that the 50/200 is 50 yards/200 meters though often gets confused or taken for granted as a 50yard/200yard, which is close enough I guess.
So my point is that how you zero may depend on your purposes.
Assuming you are using 55gr ammo, that chart will be close enough to get you on target, and you can make minor adjustments from there if need be.
If you zero your 8/3 marking for 25 yards by bottoming out and then adjusting the front sight, your 4, 5, 6, 7, and 8 marks no longer really mean anything because your bottomed out 8/3 will be a 375ish yard zero rather than a 300 meter zero. This isn't really a problem if you are only worried about the competition shoot distances, and plan on using the 25 yard zero (with crossover at 375ish yards) to aim for point of aim/point of impact on the 360 yard target, and use a little guess work for holding low on targets closer than that.
Or, the really easiest thing is to have a magnified optic with bullet drop markings for a M16 with 55gr ammo, which may not be allowed in the competition?
I'm betting you'd be shooting from a sitting, kneeling or prone position.
Hitting a 10" plate from 360 yards from the standing position with open sights is not an easy shot.
Not to derail the thread, but Moosey, what is you qualification?
Semper Fi, do or die
Expert, of course. 231 on table 1, 97 on table 2 (out of 250/100 respectivly) for 327/350
Josh, why were you shooting standing at 500 yds, in boot camp?