So I took my new to me Colt A3 Tactical Carbine out today to set it to BSZ. I measured off 25m and set up a target. After a couple clicks up and to the right I was getting a tight group pretty much at the center of the X. I then set up the same target at about 50m. I was sighting through the small apeture and noticed at that range the groups were okay on the windage, but were shooting high (maybe an inch or so).
Is this normal after you set BSZ, or is it a failure on the part of the operator (me)?
Go find a copy of the Training Manual TM-9 on the old AR-15 site.
Basically, there is confusion between BSZ on the A1 and the A2 M16/AR15's. Then to add to the confusion, there is the two apertures, long range and short range.
What you want is to understand how the line of sight and the trajectories intersect. They meet at two points, when the bullet leaves the bore below the line of sight and meets the LOS at the short zeroing range then it rises above the LOS and intersects again as it is dropping at the longer distance (battlefield zero).
Try doing a search on this AR-15.com site for "Santose Zero", an improved method to get the bullet zeroed at approx. 50yds. and 200yds. which is a more practical way of knowing your sights because the trajectory of the M193 is going to meet the LOS at 50 and 200yds and will impact within an inch at all distances from about 30-250 yds.