Almost 60 days later, I finally get my Hearn Coehorn. Sheesh, they are slower than Christmas, literally. Good thing I wasn't in a hurry, lol. I'm taking the barrel down to my machinist to drill the vent hole and liner. I use 1/8" green fuse. From what I have learned here, I'm going to instruct him to do the following:
1. Drill vent liner through dimple on outside and thread for 9/16ths grade five stainless steel bolt. The hole in the bore should be .400” from face of breech of the bore.
The hole may be angled so that it is .400” from the face of the breech of the bore. To drill the hole, the machine shop may use a piece of round stock that fit the bore snugly to hold the barrel. By trial and error, set the bar up so that the drill hits the center of the vent dimple when the barrel is slid over it until it bottoms out, and so that, with the barrel removed, it hits a point .400 from the end of the round stock.
2. Center drill the bolt with a 5/32nds bit. Remove head from bolt and cut a slot for a screw driver so that the bolt may be removed. Ground the bolt at the tip to roughly match the tip profile of the 9/16ths bit.
How does that sound?