I have a 7 3/4 size melon, i had tried on helmets locally that were way too small. But i took a chance and ordered this one last year,
http://www.airsoftpeak.com/fast-ballist ... 10181.htmlAnd it fits me perfectly, i actually have to tighten it down about 1 turn. The chin straps don't fit me at all, the chin part, sits on my cheek at full extension.
I have my replica comtacs with the rail attachments on it, and it's comfy and works well. I bought the helmet because for some reason, i was always getting shot in the top of my head, so now it doesn't hurt so bad.
It's lightweight, but it does get hot in it. In the winter it's perfect. Summer it's a little to warm. But does have some nice head band wrap to act like a head band and wick up the sweat.