The upper and lower fit together so tightly that I can turn it upside down with the barrel in the upper receiver and no pins inserted and the two will not fall apart unless shaken vigorously.
I also got some pin gauges to measure some of the bolt carrier dimensions (bolt shoulder support, gas ring run, bolt tail seal, gas key) and to measure the take down pin holes.
I have not measured all my carriers but the radian measured .5015 at the gas rings (spec is .500) and .2525 at the bolt tail.
I have an upper that will take .2535 pin through the takedown holes which is crazy loose. It's interesting what you can find when you have the tools to measure things.