Everyone is always asking about zeroing/shooting at 25 yards I think I finally have an answer on how it can be done.  Though it is not recommended you zero @ 25yards, this is great to know of you like shooting at that distance - like for the Schedule C Qualification Course; or only have access to a 25 yard range. Preferred zero is the 50 yard/200 meter Improved Battlesight Zero (IBZ) by LTC Santose.

For A2 Sights:

In any case (for shooting or zeroing) you will need to have your A2 handle setup for the IBZ (-2 clicks below 8/3).  Remember if you have a detachable carry handle your elevation adjustments are twice as fine so be sure to double all 'click' values (i.e. 2 clicks become 4 clicks).   If you have already zeroed with the IBZ then to get a 25 YARD zero set your elevation wheel as indicated:

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)

If you are ZEROING your rifle (again not really recommended), after setting up your rear sight to bottom out at 8/3 -2 (or 6/3 -4) adjust the rear sight to the values indicated above.  That is rifles will be set to 4 +2 clicks and carbines will be set to 4 (4 being the 400meter setting).  Zero your rifle at 25 yards.  All elevation adjustments for zeroing will be using the front sight.  Once you are done the numbers on the elevation wheel should be correct.  If you bottom the sight out (at 8/3 -2) you will have roughly the 50y/200M zero of the IBZ.

Note these sight settings were discovered using M193 (specifically Winchester Q3131A) at 500' ASL and about 70 degrees. Using slower comercial .223 may produce different results for zeroing, but should be good enought for shooting/plinking/qualifying at 25 yards.

For ARMS#40, other BUISs, and A1 (no elevation adjustment) Sights:

Rounds should strike 1.2" below the point of aim.  Measure for the COM of the aiming point to the center of the shot group. (keep it between 1" and 1 1/4" and it will be fine - confirm at 50y or 200M as soon as possible).

Another option with a carbine length sight radius: shoot point-of-aim = point-of-impact at 25y, then adjust the front sight up 2 clicks (to push the shot group down).  This will also give you an approximate 50 yard zero.  This trick can also be used, in reverse, on carbines that are zeroed at 50y when shooting the 25y qualification course (go down 2 clicks to shoot the course).

For Reflex/Reflex 2 Sights:

Assuming you zeroed the Reflex sight as indicated by the manual (@25meters then down 2 clicks).  You can get a 25 Yard zero for qualifying by going up 1 click (or get a rough zero by zeroing at 25 yards and only going down 1 click).

When shooting the .22 conversion kit (I use the Federal copper plated hollowpoints commonly sold at Wal-Mart for $9/box of 550 loose packed). I find the standard 300M zero of the Reflex to be dead on at 25 yards (no adjustments needed), using a 14.5 Bushmaster M4/AK rifle (16" barrel should give similar results).