I've always zeroed our M4's with 16" barrels, both iron sights and red dots at 50/225 yards. My Mk 12 has a scope so it's zeroed at 100 yards. It has adjustable turrets so I can adjust for longer ranges.
Now I'm playing the AR15A4 game. It has a 20" barrel (w/plastic handguard and free float tube/sleeve) and I use the removable A4 carry handle for the rear sight, no optic or red dot. This is a range toy and a general fun gun. I'm not sure if I should stick to the 50/225 yard zero or use a different one because of the added velocity of the longer barrel. The range I shoot at mostly is only 200 yards.
This is becoming my favorite AR/M4 platform rifle/carbine to shoot. It's a blast.
NYH1.
