brass inserts
 

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Rick,

there was a time when I used to make those inserts out of once fired .50 caliber BMG cartridge cases that were hacksawed in half and the length depended upon the size of the vise jaw...

I used to make the vise blocks out of either hardwood or acraglas with a wooden backing and obtain a crush fit on the aluminum or copper inserts to a roughed out wooden channel.

I have also made them out of copper tubing at times... but I have never taken a Luger barrel out, only revolver and rifle barrels...

I would guess that the softer varieties of aluminum are what would be optimum.

My barrel vise was made from .5 inch boiler plate and was shaped like a large rectangular box about 5 inches deep with feet that bolted to the workbench... the blocks were put into the top of the rectangle and at the bottom was a 2 ton automotive hydraulic jack that applied the pressure to the blocks around the barrel. Then I applied my receiver wrench to the rifle action and with a 3 foot handle made of one inch steel dowel, one grunt and the barrel would break it's sieze and unscrew...

revolvers were easier. once the barrel was clamped in the hydraulic vise, you just stick a hardwood lever the same size as the cylinder hole in the frame through that hole and turn (after remembering to drift out the retaining pin on those early S&W's)

real brute strength gunsmithing - huh?

we are talking 30 years ago on a young soldier's salary. Crude but effective!

Good luck.