DoOoOodsteven, please use proper grammar and punctuation, and make more useful posts when you do. I believe you need to reread the Rules and Introdution Guidelines,
this is your final warning. A 400' headshot is nothing to brag about no matter who you are, headshots are painful to other players, and frowned upon as far as I'm concerned.
The maximum effective range of a field legal Airsoft rifle is 100-110 yards, I have found the most effective BB to be a .36 gram Straight or Madbull. Anything over 100 yards is luck, and a combination with amazing shooting conditions.
I have never cared much about my longest shot, I will always always remember a shot I landed on a guy who didn't hear it at all, and was unsure of what hit him. He stopped for a while and then moved on. It sucks because you can see the impact on their clothing, like poking a sleeve or pant leg with your finger. They would be dead in real life, but unfortunately you need to make another decision to shoot or not.
Classic picture from a field here in Michigan, I was engaging people at the woodsline, and on top of the ridge beyond that. To the top of the ridge was I'd say 80 yards, through canopy brush.