What tools are required to use a finish reamer?
A finish reamer, go and no go head space gages, a 12 in. 3/8 drive extension, and a tap handle.
Once the propertly chambered or pre chambered barrel is screwed on the action. Strip the bolt of its firing pin, extractor/ejector. Put check the headspace by putting in the "go" gage. The bolt shouldn't close.
Put the square end of the finish reamer into the female end of the 12 in. extension. Carefully side it into the chamber. Use the tap handle over the male side of the extension. put cutting oil on the reamer and carefully add pressure as you turn the tap handle. After a couple turns bring out the reamer, clean it and the chamber of chips and re-check the headspace with the go gage.
Keep doing this until the bolt barely closes on the go gage. Check with the No-go gage, you shouldn't be able to close the bolt.
It's slow (slower then using a lathe) but its work, and with care you get a nice tight accurate chamber.
Some people use a "field" gage, which is a bit bigger then the no -go gage. I don't even own a field gage. If I can close the bolt on a No-go gage, I set the barrel back and start over.