school me on the a2 rear sight

[ar_mcadams]

On a m4 carry handle a2 rear sight you have two apetures, small hole and large hole marked 0-2. I have allways used the small hole but my question is if you are dead on at 100 yards with the small apeture, where will the bullet impact be if you flip to the large hole but dont do anything else to the sight? Is there actually a difference between the two other than the size of the hole? Im trying to understand the IBZ method. When I tried it today my point of impact went to the right several inches and down when I flipped to the large hole.

[DRich]

The two apertures on the A2 sights are on different planes. Switching from the small aperture to the large aperture will shift the POI.

From XS Sights:

Comparing some of the rear sights available today there appears to be 3 variations available. The 1st style (and oldest) has a .014 offset. This gives a 2.52 inch shift in point of impact at 100 yards between the two apertures. The 2nd style has a .017 offset, which shifts point of impact 3.06 inches at 100 yards. The 3rd style has a .024 offset giving a 4.36 inch shift in P.O.I.

All of the points of impact shifts shown above are for the standard barrel AR-15/M-16 that has a sight radius of 20 inches. The shorter sight radius (14.5 inches) of the M4 carbine and weapons of similar configuration increase the amount of point of impact shift. The shifts for these shorter sight radius weapons are 3.48, 4.25, 5.96 inches respectively.

[ar_mcadams]

thanks