Are all hanger bars the same as far as bolt locations for the forearm? Or does every manufacturer have there own specs. How do they compair lenth and width? Can they be interchanged.

They might be slightly different, but have been able to interchange them with out any problem.
Rich Jake

I have a VVCG .223 barrel, and a Pachmayer forend fits the hanger bar fine.

Thanks for the info.