Need help zeroing an AR

Getting back to the original question, if I remember right there is a happy crossover point near 200 yards. If zero at 25 yards, it should be zero at 200.
Of course this is based on certain ammo, so a happy crossover point might exist in your case before or after that 200 yard mark.
Some research on ballistics for your brand of ammo should give you a crossover point using a 25 yard zero.
 
Here's some selected text found on the subject from a a different forum and then the URL if I do this right
"The path to unraveling the mystery begins with understanding the trajectory of the 5.56mm bullet in flight from the rifle's muzzle until it impacts a target. When you aim the rifle sights at a target, the line of sight is a straight line through the rear sight aperture, over the front sight post then straight out to the target. This is known as Point of Aim (POA). However much like a 50-yard football pass, the bullet travels in an arc, not a straight line, and wherever it hits is known as Point of Impact (POI). The trick is to get the straight line POA to equal the POI on that arc - and have it happen dead center on your target. At the muzzle the bullet is about 2.5" below POA because the sights are about that much higher than the centerline of the barrel. But the bullet soon rises above POA then downrange it falls back below POA. Depending on the rifle's initial angle of elevation you can expect a bullet to crossover the POA twice, once around 25-45 meters as it rises above POA and again around 200-300 meters out as it falls back to earth. Ballistics of 5.56mm bullets are well understood and the arc or trajectory is consistent if the rifle and ammunition and rifleman are all up to par. Understanding the bullet trajectory allows you to zero in the rifle at the closer crossover point (where POA = POI) and expect that the second crossover point also will be in zero, again POA = POI. The advantage is you zero at a shorter range, even a pistol range, with confidence that your long range zero will be true as well. Still, check that long range crossover on a day when the wind is calm."
http://www.ar15armory.com/forums/lofiversion/index.php?t69085.html
 
Mobuck has it.

Besides the which, when I tested four ARs in various configurations with four different sighting systems and four different bullet weights, some loads impacted as high as 14 inches above point of aim at 200 yards when zeroed at 25.

You can't make a valid one-size-fits-all claim that a 25-yard zero will put your gun and your load right where you want it at 100 or 200 yards.

Zero at 25 to get on paper, then zero at 100 or 200 yards for a realistic expectation of hitting at those distances.
Denis
 
True there are all sorts of oddball sighting choices and barrel lengths found in the AR type platforms. I call these Franken-Rifles. You zero at 25 and are 14 inches high at 200 and you have things out of whack and outside the scope of my info. My info is based on having a legitimate or genuine military type setup. If that is not the case then you are left o sighting in as needed or figuring out why it doesn't work as needed. From what you say, it sounds like your rifle is pointed sky high and your sights are not about 2.5 inches and inline with the bore.
 
"When someone asks advise about guns responsible answers are in order".

No one gave him a irresponsible answer.

So far everyone but you has told him the way it is.
 
The "sight in at 25 yards and you will be on at 200" is a rule of thumb. It may or not be true on the M-16 A2 or AR-15 rifles with the same sighting system.

Even if it works out that your elevation is correct at 200 your windage could be off.
You need to zero at the distance you know you will most likely to shoot and shoot enough at various ranges so you know how much to hold over or under or how much elevation to click if you sighting system allows it.
 
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Load it in the chamber, use it to sight in indoors, should at least get you on paper and you can then use trial and error and a coin to adjust the EOTech's reticle until you are on paper at your desired range.
 
Chick,
One stock 1984 Colt Sporter A2, 20-inch Gov profile barrel, 1/7 twist, iron sights.
One stock (aside from grip replacement & one-inch stock extension) 1994 Colt Lightweight Sporter, 16-inch pencil barrel, 1/7 twist, 4-power carry handle scope.
One Colt ARA3 mid 1990s, 16-inch heavy barrel, 1/9 twist, ACOG on flattop rail.
One 2011 Stag Model 3, 16-inch standard barrel, 1/7 twist, Aimpoint on flat rail.

All four with 5.56 chambers.
Four bullet weights from 50, 55, 68, 77. Good quality commercial stuff.

All four rifles zeroed initially at 25 yards.
All four then fired at 50, 100, and 200 yards.

All four rifles impacted differently from 50 on out to 200.
The 20-inch Sporter A2 had the least rise at 200. The shorter guns ran from 10-14 inches high at 200 with some loads.

Velocities, bullet weights, and sighting plane heights can all create quite a difference in POI between different guns & loads.

You want to hit at 100? Zero at 100. You want to hit at 200? Zero for 200.

I'm not talking about striking "somewhere" on a human torso, I'm talking about hitting a grapefruit-sized target at those distances, without having to use either several rounds to "mortar" them in, or use a "best guess" sight picture.

Sight YOUR gun in at YOUR distance with YOUR load. Don't buy the generic 25-yard zero nonsense, your gun & load may surprise you at longer distances, and not in a nice way.

Denis
 
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