So I just about finished gathering all the pieces needed to put together a left handed AR. I acquired a left handed black rain ordnance upper, a standard black rain lower, left handed black rain ordnance BCG, etc... The only thing left for me to purchase is a barrel which I wanted to go with a Criterion Hbar barrel. I had ordered one from Optics Planet some time ago which was all rusted, but now I want to order directly from Criterion. Am I correct in assuming a standard barrel will work or do I need a special barrel made for left handed upper? I keep reading conflicting reports about barrel extensions? Any experiences?