Hey all pretty new to the AR 15 world and recently bought my first Bushmaster AR 223-5.56 with an Eotech sight. Ive already and only got it sighted in at 50 yards. My question for all with experience with an Eotech sight is whats a good rule of thumb sighting them in as far as distance? I was thinking 200 yards seeings how the bullet raises when it leaves the barrel and then lowers, but would be hard for me to see at that distance to sight it in. Any suggestions? What has everyone else done? Thanks

Umm no....bullet will begin to drop as soon as it leaves the barrel.  That's called gravity.

http://www.chuckhawks.com/bullet_trajectory.htm

Explain how when sighting in at 25 yards you have a height over bore distance of let's say 2". So you aim at the target center but it hits 2" low while at 100yards it's dead on.

I sight in all my ars this way. Given different bullet weights do different things but it still roughly the same outcome. Seems like it does rise and then fall some to me.

the trajectory of a 5.56 is somewhat of an arc.
I personally like to sight my irons and optic at approximately 100m...then get familiar with it at 50m, 30m, 15m and 200m (not necessarily in that order)

Ask yourself why is it an arc?

Since eveyone seems to be dancing around tha actual answer... check out the FAQ:

Combat Zero has some good information on effect of zerong at various distances.

Effect of zero distance 55g ammo has good graph/image showing the trajectories.

Since the sight is higher than the bore, if you zero at 50 yds/meters etc the bullet has to travel up to impact the line of sight, so the sights will be set up with the barrel pointing slightly upwards from horizontal.  At 100yds, the bullet will hit higher than the point of aim since it is still in the upward part of the arc.  Around 200 yds it will be dropping back down to pint of aim (line of sight when looking though sight).  So you will dead on (point of aim is same as point of impact of the bullet) at both 50 and 200 yds (rough numbers, read the FAQ's for real details).  Between 50 and 200 it will impact above your point of aim.  Less than 50yds or more than 200 yds it will impact below your point of aim.

Typically you would set zeor at either 33 or 50 meters (again, check FAQ's for specific details) and then it will be "combat accurate" at a wide variety of ranges (ie. only off one way or the other by and inch or two from 25-300 meters).

My Eotechs are zerod at 100, just because my ranges are 100.  One day I plan to set them for a proper "Battlesight Zero"....

Because gravity is constant :)

Watch this 50 yard ar15 zero video.

Then use these calibrated red dot targets and go for it.

Gravity will affect the bullet at 10m/s^2. Now your scope is mounted above your sight plane and has two intersections points on the fall of the bullet. REPEAT AFTER ME THE BULLET DOESNT RISE

Or you're slightly elevating your weapon when you sight it in?  The bullet does not rise from the muzzle and then arc down.  The other posters linked some good info.

For clarification on the idea of the rising bullet, see the illustration in the first post of the following link.  In short, the trajectory of the bullet meets or crosses the line of sight because we point our barrels upward.


http://www.ar15.com/forums/t_3_18/512335_AR_15_Zeros_and_Trajectories.html

Thanks, that gravity is a heartless bitch