When I read the OP's description of using the supplied headspace gauge as a go gauge, it immediately reminded me of my own recent RimX project. I fitted & chambered a Bartlein bbl for my RimX, and initial results on target were more than a little disappointing - plus I had several failures to eject. A call to Aaron at Zermatt Arms resulted in him stopping me short right after I told him I set headspace using their gauge so the bolt would just close on it. That gauge is intended to be used as a no-go gauge, which is why the rim of the gauge is .052" thick. Using it as a go gauge will result in at least .010" excess headspace, which will produce inconsistent ignition to say the least. After our conversation, I pulled the Bartlein & set it back .010", which resulted in a big improvement in groups - although I was still having issues with failure to eject. I couldn't see anything wrong with the ejector, and sent a close-up photo of it taken with a macro lens to Zermatt. Aaron & Ray concurred, so I went after the tensioner with a set of white ceramic stones, putting a radius on the bottom inside corner of the tensioner's hook, as well as a very slight radius in the back inside corner of the hook, thinking that would allow case rims to slip up fully into the ejector & tensioner. What I believe was happening was that the edge of the hook of the tensioner was protruding far enough to be hitting the case body, and stoning the radius in the hook itself & in the inside/back corner of the hook alleviated that contact and promoted better interaction between the case & the tensioner. So now, not only was the rifle shooting more accurately, it was also suffering far fewer failures to eject. I went a bit further with the radius on the tensioner hook than I intended; it's working great right now, but I'll watch for issues as the round count builds. Ray sent me two new tensioners - one with no extra work done on it, and one with a slight radius stoned, similar to what you see in the attached photo. If my tensioner eventually fails, I'll blame it on my exuberance with the stone, and simply replace it with the modified tensioner that Ray sent me. The good thing about stoning the tensioner is that it's easy to remove, and just as easy to replace back into the boltface.
After doing the .010" set-back, I wasn't seeing any engraving of the front driving band of the bullets after chambering & extracting a loaded round, so I pulled the bbl again, and this time, set it back .070", then running my EPS reamer in to the point where the rim portion of the reamer (which features a .010'-.015" radius ground at the body/rim junction) was just starting to cut the breech at the chamber. I now have a good deal of engraving by the lands in the leade on the front driving band, and accuracy improved significantly.