Does anybody know why this particular military manual requires the rear sight of an M16A2 to bottom out at 3 clicks below 8/3?  The manual says that point of impact at 36 yards is the same as 300 yards.  Why not just have the rear sight bottom out at 8/3, and leave it at 8/3 for shooting at distances of 36 yards & 300 yards?  I'm sure the Corps must have a good reason for it, but I just can not discern it.

(Edited to correct a punctuation error).

I don't know how "new" this method is since it is the way we were instructed to use the A2 when we transitioned from the A1 back in '85 or so.

By setting the rear sight to 8/3 -2 and adjusting elevation on the front sight post to obtain POA=POI with the small rear sight aperature at 200yds/m, the rifleman will be able to then set the rear sight to 8/3 +/-1 to obtain a POA=POI at 300yds/m, at 400yds/m 4 +/-1, at 500yds/m 5 +/-1, so forth and so on out to 800yds/m.

Also, with the rear sight set to 8/3 -2 and using the large 0-200 aperature, the rifleman has a very flat 0-200yds/m zero that is fast and easier to aquire in a high stress close range encounter.

Remember, the USMC KD range is very similar to a service rifle match, but the targets are a bit different and the scoring was changed, about '96 if memory serves, to a hit/miss type of affair, after all, in combat only hits count.  Whereas Match shooters require a higher/finer degree of sight manipulation, hence the 1/4 and 1/2 MOA clicks found on Match rifles.

There is an excellent resource here:

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

and if you select the very first one, Improved Battle Sight zero by LTC Santose, it will give you a very usable setting which is more easily attained since American ranges generally all have a 50yd line you can use.

Their main page is here:

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

and has a wealth of information. It isn't nearly the forum this is however I'd say it is an excellent reference source.

Close, but not quite right.  To use the LARGE aperture to a 200M zero you need to have the elevation wheel set to 8/3.  The large aperture is at a different elevation than the small aperture.  Set the dial to 8/3-2 for the SMALL aperture to get the 200M zero.

If you set the dial to 8/3-3 (with the small aperture) you get a rough 100M zero.

So by allowing it to bottom out 3 clicks below the 300M setting you can get zeros at 200M (8/3 -2) and 100M (8/3 -3) using the small aperture.

Just slightly off topic here, but I've got to ask.  Sorry if I'm hijacking the topic.

Right now my sights are set using the Improved Battle Sight zero listed on the Maryland page.  The rifle is zeroed at 50 yards with the small aparture and -2 clicks just like the procedure says.  

If I set the rear sight to 8/3 and use the large aparture, I should have the same POI at 50 yards, right?  With this setting I'm 3" low.  Any suggestions?
Scott

Correct.


Not uncommon at all.  Some people do have a problem using the large aperture and shoot low (I was one of those - I had to practice to 'get it right).  Also, it seems not all parts are created equal.  If you go to Ashley/Express/XS (whatever they are calling themselves theses days) website you will find a FAQ on this (FAQ #10).  They have found at least 3 different A2 aperture setups all with differences in the change in impact.

Proper aperture should have the same difference as 2 windage clicks (or 4 if its a detachable handle).

I know of no easy way of determining what the difference is until you fire.  Nor do I know which the different manufacturers use (or if they use a variety).

I avoided the problem by just buying the XS Same Plane rear aperture.  Both apertures are on the same plane so there is no change in the point of impact when you switch.  There are two probles with this solution:
1) Cost (about $30)
2) the apertures are larger than the military ones (fine for the large aperture but I don't like they also increased the size of the small aperture).

Thanks Forest.  I figured I would just shoot it a little more to make sure it was the sight.  If that is the case, I'll just add a few extra clicks when using the large aparture.
Scott