Okay, here is some additional information as well as some irony! Yesterday, I finally got around to installing and shooting my Muller Octomax barrel. Ironic it was only a day after the OP got to shoot his. As far as information, that barrel is tight! I could tell the first patch I ran down it. The day was anything but optimal for testing, but I plan on shooting the rifle/barrel combo this weekend at an indoor match and at least needed to get the rifle sighted in. With the wind nixing any hope of proper tunning procedure, I just spun the tuner out to 175 and shot, waiting on the flags. I only did 5 click outs on the tuner and finally ended at 195 and things looked better. I shot a partial card while doing this and after I was kind of satisfied with how the gun was shooting the shots that were shot for score were very good. Especially considering wind, not a finished tune, and I only shot one lot of ammo, 100rds of 2019 Eley 6 machine Match. Now results this weekend will NOT tell me much more, as indoor IME, is way more ammo dependent than outdoor, but I'm still going to shoot it. I will reiterate, that barrel is tight. The initial patches before the barrel was shot were tight. They were even tighter after 50rds fouling buildup in the bore.
Scott