I found D bit cutters while looking for methods of chambering the Welrod without buying a reamer. After cutting the profile in a collet chuck I swapped to a 4 jaw and dialed in a .010” offset to cut the back relief. Then milled out half of it on the mill. The front section is a guide which is why I didn’t mill half of it off. Made this one out of O1 tool steel and hardened with a torch. The chamber finish came out decent enough for my uses.