I have built a number of barrel vises for myself and friends over the years.
I just take 1.5" steel, bolt two pieces together with a 0.15" spacer, and then drill and bore a 1.5" hole.
I buy lengths of 1.5" round 6061 Aluminium rods:
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I put 1.5" lengths of the rods in the lathe and bore them out to fit the barrel.
Some get tapers.
I cut slits in the bushings.
Some bushings get cut in half.
I bolt the barrel vise to a 300 pound steel bench.
I clean the barrel with alcohol, unless it has wax on it.
I started out using Brownells rosin on the barrel.
Then I used powdered sugar.
Now the wife has suggested to me that the coefficient of friction with corn starch is best.
I started out with 1/2-13 bolts, but even grade 5 were snapping off with rusty military barrels.
I switched to 7/8-14.
You will need that tooling for making reloading dies anyway.
I am an amatuer gunsmith, but Randy Ketchum is a pro. He made his barrel vise with a huge hydraulic jack on his heavy bench. He can get the barrel in and out fast.
Meanwhile I am left pulling on a 3/4" drive 3' long socket wrench to tighten and loosen. I can put as much as 600 foot pounds on the action wrench and not get barrel slippage. That is needed to pull rusty old surplus barrels.