I have a Bush Master M4A3. The iron sights are on a detachable carry handle. It gives directions for sighting in at 25 meters for close combat. I understand the procedure, but the shortest riffle range around here is at 50 yards. If I use the same procedure to sight in the rifle on the 50 yard range as described in the 25 meter directions, will the grouping be off at 25 meters?

 I will be using the rifle in carbine matches. Thanks for any input.

You are MUCH MUCH better off sighting that rifle in at 50yards.  The trajectory is much flatter and if you do it right your elevation wheel will be properly calibrated.

Details are here: Improved Battlesight Zero (IBSZ)

Thanks for the info. The sight was exactly what I was looking for.