Reading what Nagell has written, the barrels would be finished and that appears to be in or on the monoblock.

As for cutting by hand, it is something that is done, often.

You ran your lathe in back gear because that is the slowest speed.

The nature of all reamers is to cut over or oval as you call it. This is the reason some of us use a fitted removable bushing that is our pilot riding on top of the rifling.

As an aside Sir, barrels are sold short chambered every day, just for the purpose of cutting the finale for headspacing, also pre-threaded. Does this mean you have to have a mill or converter for your lathe to cut the extractor groove? No Sir, I still cut by hand, while my mill sets idle.

Just as some cut a chamber in the head and some cut the chamber on a steady rest, there is other ways to cut a chamber, that does not require a lathe.

Depending on the mill, one could cut the chamber using the proper mill. Using an indexing, dividing head, this is exactly how I cut revolver cylinders on my mill.

Yes Sir machinery does make many jobs easier. All machines are meant, and made to do is replace a hand operation. Just as many of us were taught in our school day.

With due respect Mr. Bramble, there is more than "one way to skin a cat"!

Just as there is other ways of saying 375.

Respectively your, 3sixbits.