After 3D printing a plastic 1:10 barrel I decided to have a go at turning one in steel. I had a length of steel 70mm diameter and 290mm long, which was just too short to turn the entire barrel, so I decided to make one of the breech reduction rings separately, when I make the cascabel.
I did not know what the steel grade was, but it was off a machine so I thought that there would be a good chance that it would be reasonable quality.
The turning was initially fairly routine.
I experienced 2 problems with the CNC turning. The tapered chase of the barrel, and the rounded fillets came out really well, but the straight sections of the breech developed chatter marks. I was preparing to take a skim to remove the chatter marks when I bumped the manual CNC control, the cutter dug in, and I got a deep score in the breech. And broke the carbide cutter. I turned away the dig in, but it left the breech diameter 3.5mm undersize.
I have no more steel of that size, and it will be quite a while before I get an opportunity to buy some. So I persisted with the slightly undersized barrel. It will be 62mm diameter rather than the intended 65.5mm. I still have not decided whether to scrap it and start again. But if I can get some more suitable steel I will remake it. I might even use the undersized barrel to make a 64lb Armstrong RML, which had a smaller diameter breech than the 80lb RML which I am making.