New, ... this is a rather expensive experiment, but most are, like wasting Berger 300 gr bullets in a 8.6 blackout because they are accurate. ...Why hold back on performance? Performance...Thats why I "go there" in the first place...full throttle, on a race car, to see what it's got..checked the headspace before and after use, so far it's the same, on both calibers used. I have a new Bartlein barrel for the 6.5 Creedmoor, so I'm not concerned about its barrel and check the progress of its wear ...so far everything is good. Burn less powder at higher pressures probably close to the barrel life of the medium 6.5/ 264 Mag calibers in existence...maybe better.