Sighting in an AR15 w/ A2 sights

[TarpleyG]

Can someone please answer why we do battlesight zero this way? Below is text from the U.S. MARINE CORPS 25-METER ZEROING PROCEDURES from the M-16 manual. Why do you dial the rear sight all the way down then back up one click (to the Z) to zero in at 25yds? Why not just leave it all the way down? I followed these instructions and got my rifle hitting POA at 25 metres using the small aperture. When I switched to the large aperture and moved the elevation knob back to 6/3, my POI was low at 25 metres.

Greg

4 ROTATE ELEVATION KNOB IN THE DOWN DIRECTION (COUNTER-CLOCKWISE). THE ELEVATION KNOB SHOULD STOP THREE CLICKS PAST THE 300-METER MARK. THE REAR SIGHT SHOULD BE ALL THE WAY DOWN ON THE LAST WHOLE “CLICK†BEFORE IT BOTTOMS OUT. THIS IS CALLED MECHANICAL ZERO ELEVATION FOR THE REAR SIGHT. IF YOUR RANGE SCALE WILL NOT LINE UP IN THE ABOVE MANNER, AN ARMORER WILL BE REQUIRED TO ADJUST THE RANGE SCALE FOR YOU.

5 NOW ROTATE THE ELEVATION KNOB "UP" ONE CLICK PAST THE 300-METER MARK. FROM THIS POINT ON, THE REAR SIGHT ELEVATION KNOB SHOULD NOT BE MOVED. ANY CHANGES IN ELEVATION REQUIRED IN THE FOLLOWING ZEROING STEPS ARE MADE TO THE FRONT SIGHT POST ONLY.

 

[444]

http://groups.msn.com/TheMarylandAR15ShootersSite/zeroingmethods.msnw

 

[Blackhawk 6]

You followed the zeroing procedure correctly for a three-hundred meter zero. Your small aperature is zeroed for three-hundred meters. This is the zero the military uses. If you rotate the wheel under the rear sight to 4, 5 or 6, your point of impact will (roughly) be adjusted for targets at these ranges.

If you look at the base of the large aperature you will find that it is marked "0-2." The large aperature is centered at a different height. When using the large aperature you should be approximately 1.5" low at 25 meters, giving you a two-hundred meter zero (with the rear sight set on 3/6).

 

[TarpleyG]

That is exactly where it is hitting now. Just wondered what the logic was behind all that. Now, say I am using this for primarily 3-gun stuff out to a maximum of 25-35 yards, where would you all set your sights to?

Greg

 

[Blackhawk 6]

Leave your zero as it is. Use the large aperature. You should be within two inches of your point of aim.

 

[Bartholomew Roberts]

I'd ditch both zeros and use the IBZ (zero at 50yds). It is described in the link to the Maryland AR15 club and gives a nice simple flat zero that keeps you within 2" of your point of aim from 0yds to 225yds.

However, the zero you've got will work fine for 3-gun at 25-35yds, just use your large aperture and remember to compensate for the height over bore at close range.