I'm currently building an AR and thinking of going with a 20" upper, and I'm trying to keep it light, so I really want a pencil barrel. Unfortunately, it doesn't look like any of the top-tier manufacturers make one; BCM only offers government profile, and DD and Spike's don't even make anything with a barrel that long. Are they ANY top-quality manufacturers that currently offer 20" lightweight uppers, or do I have to buy a used Colt A1 upper or have a gunsmith put something together for me?