Poor accuracy is almost always the result of using poor ammo. FMJ bullets are the worst available because they are made backwards, from the pointy end to the base. That leaves an open base which is detrimental to accuracy.
I only have one BCM barrel, a 20" A2 1/7 twist chrome lined copy. It shoots okay, 1.25" to 1.5" with match ammo at 100 yards. Nothing to write home about.
Barrel quality nowadays is better than it's ever been. Buy a stainless steel barrel from White Oak Armament, Wilson Combat, Noveske, Lilja, Shilen, Compass Lake Engineering, Lothar-Walther or Criterion. You'll get a great barrel, some of them for around the same price as BCM.
If you plan on shooting nothing but cheap FMJ's don't waste your money or time on a premium barrel, they won't make bananas fly straight.
Heavier buffers work for slowing down over gassed rifles.