I know it's a little late, but hopefully this helps other folks.
I have three proof carbon bbls. A 16.5" 6.5 Creedmoor bolt gun, a 16.5" AR in 5.56 wyld, and a 22" 300 win mag.
All will shoot 1/2 MOA or better (I have dropped in some groups around 1/4") 5-shot groups with the right ammo and me doing my part and they will do it on day one if you know what your are doing with your loading practices, but I can only get the AR to do it if I load beyond magazine length which isn't practical. At mag length with Lapua brass and basically no prep, the AR shoots around .8". If I work on it, I could probably get that down more but it's an AR so I haven't put the time in.
I don't shoot enough to worry that much about the barrel life. Maybe put 300-500 rounds through each and I haven't seen any degradation and some of my stuff is pretty hot. If anything, my group sizes have gotten smaller the more I shoot because I'm getting better.
A huge pro for me is that a steel barrel will get so hot it will boil water/burn you. The carbon barrel never seems to get so hot you can't touch it and I shoot suppressed. You may not want to grab it and hold on though. I don't know if it's dissipating heat faster or just insulating and holding the heat on, but either way it doesn't seem to impact accuracy.
I also like that I don't have to worry about pitting and I love the carbon look.
The only issue I have is that on the 300 wim mag, my groups will drop about 1/4 inch from string to strong as the bbl warms up. Eventually they will be about an inch or more low. Still tight groups, just with a lower POI. It's pretty predictable and comes back to zero each time. I asked someone at proof about that and they said that's normal for magnum rifles with a can on the end pushing that much heat. I don't know if that's 100% true or not but I'm ok with it because this isn't a match rifle. On hunting you aren't likely to put 15 rounds down range in less than 30 minutes. Just for reference, I'm pushing 75gn h1000 with a 230gn berger around 2750fps. I used to shoot hotter but there wasn't much benefit so I backed it off. Pretty spent after 10-15 rounds of that anyway...
The 6.5 doesn't have any POI shift even after 50 hot, suppressed rounds rounds in about 90 minutes. Likely because of the shorter bbl and smaller cartridge.
So, if you can afford them they do pretty well for the right applications. I probably wouldn't do another AR in a proof bbl just because you could probably get similar results with a much less expensive thin steel bbl, but on a longer range bolt gun, it's a solid choice especially in the mid-range cartridges like 6.5 CM.
