Dr Stan, were you an MR in the Navy? Noticed the insignia. I was an MR.
Yes I was. August 17, 1973 to August 16, 1977. Discharged as a MR2. Two WESTPAC's one on the USS Coral Sea CVA-43 and the 2nd on the USS Samuel Gompers AD-37.
Since you're already working on the mill, you could cut the barrel to a D shape using a rotary table & tail stock, then cut the rail in the straight leg of the D.