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1/25/2018 7:38:29 AM
Posted: 10/22/2002 9:27:36 AM EST
If you lower the A2 rear sight to the bottom (mechanical zero), what is the height over bore (HOB) of the large aperture and the small aperture?

Thanks for any help...
Link Posted: 10/22/2002 10:31:28 AM EST
Height over bore is usually measured by the front sight. Standard is 2.6". Though there is some variance (Colt's M4 barrels have a different height front sight - the detachable carryhandles are different to reflect this).

There should be a 2-3moa difference between the large & small aperture - however there seems to be some variance by the AR manufacturers as evidence by this article:
Link Posted: 10/22/2002 12:23:24 PM EST
[Last Edit: 10/22/2002 12:35:42 PM EST by JCraig]
Forest good article, thanks for the info.

It seem the small aperture can vary. But what about the large aperture? If the large aperture is at mechanical zero, what is its HOB? Is it 2.6" also?

I’m working on a 25 yard variation target for the Improved Battlesight Zero by Lt. Colonel Chuck Santose, for the next release of our TargetExpress software. Mr. Santose’s method sights in at 50 yards with the rear sight set to 8/3 -2 using the small aperture. Assuming flat trajectory, at 25 yards the point of impact should be ½ of the HOB.

Comments please…

Thanks again,
Link Posted: 10/23/2002 7:53:54 AM EST
[Last Edit: 10/24/2002 12:47:07 PM EST by Forest]
We already solved the 25 yard issue with LTC Santose's Zero.

Assuming an adjustable rear sight on a 20" rifle you set it to '4+2' to zero at 25 yards; or '4' if you have a carbine sight radius. Point of aim=point of impact.

But if you want to zero with the sight set to 8/3 +2 the point of impact should be about 1.2" (say an inch and a quarter) below the point of aim.

Zeroing is ALWAYS done with the small aperture for the most precise sight picture. The height of the rear sight should be a fraction higher than 2.6", the difference being measured in hundreths of an inch I'm sure. Look at the difference in heigh of the small & large apertures, its miniscule but makes noticable changes downrange.

Edited to fix brain-cramp
Link Posted: 10/23/2002 8:22:37 AM EST
Thanks again Forest,
I will adjust my targets accordingly. I'm mainly working on easier to shoot at sighting targets. Targets with alignment marks and such, ...your front site here... kind of stuff.

But we are looking for new targets to add to our software. Any ideas or suggestions are always welcome.

Link Posted: 10/24/2002 10:56:58 AM EST

Assuming an adjustable rear sight you set it to '4' to zero at 25 yards; or '4 +2' if you have a carbine sight radius.
That's the opposite of what's on your site:

For 20"+ barreled rifles (or Dissapator style carbines) set the wheel to 4 +2 Clicks
For 16" (and less) carbines (short sight radius) set the wheel to 4 (400M setting)

I think the site is right, but can you verify?
Link Posted: 10/24/2002 12:41:17 PM EST

Originally Posted By Mike_L:
I think the site is right, but can you verify?

Site is correct - poster had a brain cramp .

I will correct my post - thanks for catching it.
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