In case someone is following along I would point out that I would NEVER seat a bullet "diameter deep" if that meant deeper than the published OAL in a reloading manual.
With that out of the way, a previous post has offered that if you are loading for the AR15 you can't go longer than 2.260 without single loading by hand. Of course if you're loading for a bolt rifle then disregard...
I used the method you described at first (seating a bullet in a case sized to just barely hold the case and closing the bolt). I did it for all my rifles and all my bullets one day - okay I was bored.
I've since gone out and bought the Stoney Point gauge. It's very easy but the numbers were identical.
Now if closing the bolt on your test round leaves anything other than barely perceptible marks then the number would be quite suspect. Others on this forum use a sharpie or lamp blacking to witness the marks. I just used good light and glasses.