I just put the Mesa barrel clamp on my M4 and used it to mount a Surefire Scout Light for a night shoot last weekend and it worked great. I am very pleased with it since it seemed that after I had placed the order that it didn't appear it was even suppose to fit the M4. I don't think the fit could be any better, so not sure why their web site seems to suggest it does not fit? Oh well, something works that is not suppose to. Nice!