Ok, here’s what happened. I bought a PH Volunteer .451. It’s a real joy to shoot and so much fun. I don’t collect or own any other ML. When the lockdown began I started all those little jobs in my workshop. I had noticed that the hammer was blowing back on the hammer on my last 2 visits to the range. A spare nipple came with the gun so I decided to change it. A nipple key also came with the gun so I tried it. No dice. The nipple seems to made of a brass like material. I sprayed penetrating oil onto the nipple and down the barrel. I left it for days and repeated. No movement. I have tried every tool but the nipple has not shifted. I was left with no option but to drill it out. It’s well drilled out now, but the internal threads are not visible yet. I am waiting on a 5/16 - 18 tap. I hope to gradually tap down and try to reveal the threads and save the gun. The second photo show the ring of nipple material left to remove
That’s the short version. Thoughts?