I have a proof 6.5cm prefit. The weight vs a regular barrel is super nice. It shoots excellent now that I found the load, but it isn't like my other custom barrels either. I can't mag feed the bigger bullets without a massive jump and I couldn't ever get a 140 gr or bigger to ever shoot like I do with all of my other barrels. Not sure why exactly, or if it's even related to the carbon or what. That said, the 130 gr stuff shoots like a laser. I think if I was ordering one I'd probably try to get a Bartlein carbon with BB steel but if price was an issue, proof is pretty good. I've heard from some reputable smith's that everyone here would know that proof has had some quality control issues from time to time since they got really big and started kicking out such a high number of barrels, but they also apparently handle warranty issues well. I don't know much about carbon 6. I had a BSF carbon barrel that shot excellent in an ar10, but those are the only 2 carbons I've had.