A few companies do this, and Fulton Armory comes immediately to mind, with the "match chamber." It's not uncommon. It's not even important in the .308ARs like it is with the .223 Wylde in the AR15s - THAT makes a difference, in AR15s. In .308ARs, it's not much of a difference.
What you need to do here is call Rainier Arms, and that's why I highlighted that part above. Ask them what gauges THEY use when checking headspace. Not kidding on that part. You can run regular 7.62 NATO gauges through a good barrel, and fail that brand new barrel. You can run .308 Win gauges through a brand new barrel, and fail that one, too. It depends more on the gauges that the barrel manufacturer uses, than anything else - and how tight they cut that thing to the "GO" gauge. Another manufacturers GO gauge might be one-thou different, and it's not gonna work.
You didn't feed a NO-GO gauge,with this set. Here's what I'd do - lightly and slowly chamber a spent .308 WIn case. If it closes on it, you're good.
Or, call Rainier, asks them what gauges they use, buy or find those gauges, and retest. My $0.02 on it. Calling Rainier, and finding out that info, though - that's priceless...
Oh... ignore everything you were told on that other place - that you left the link to... There's a bunch of garbage in there, and I stopped reading it all before I got to that page 2. Your ToolCraft BCG and bolt are fine - they make every BCG that leaves Aero Precision... and alot more, for many, many other OEM manufacturers...