Here is an interesting video about the combat effectiveness of different zeroes for a standard AR firing 5.56.
Having watched competitors shoot at FNH USA 3Gun, I am always amazed at the few that shoot in limited divisions. Tac Limited or Heavy Metal divisions only allow the use of iron sights or non-magnified red dots. Shooting at long distance targets from 100-400 yard away always seemed impossible to me without a scope. However, looking at the 300 yard zero target, that Haley shows in the video below, I can see how effective it would be for engaging a 3Gun stage with long distance targets even out to 400 yards. It almost looks possible for me to hit 6-8 inch steel with just a red dot. I used to think a 50/200 yard zero was ideal but seeing the hits on the 300 yard zero is changing my mind. What do you zero your AR at?
The original video I posted was taken down. Here is a link to one on Facebook.