Lizard- Thanks for all that good info. I remembered the GRRW machinery going to Montrose, Neill didn't say that. I was wrong, but I was close, Grand Junction is nearby.
I have a Stylus 3 Streamlight that I look into bores with. I filed the rotary turn-switch down to .398 diameter so it will drop into a .40 bore. It won't go into my .40 Green River. It does go into 3 Green Mountain bores loosely, maybe a little snugger into a Douglas, and a little closer fit yet into a Rice barrel.
Just checked my new GRRW .58 1-60 bore, it is very smooth and has very fine striations on both the lands and the grooves, if I look hard. And my .54 GRRW bore I'm building now is the same. I have not slugged the bore, so I don't know its exact diameter. Another .54 GRRW Hawken I built up is also very smooth, and uses a .530 ball. I'll have to study them closer to see how the marks go.