I just removed the breach plug from my Richmond Carbine.
The first thing I tried was to grip the barrel in my vice with leather. That earned me some vice marks in the side of my barrel. It could not grip the barrel tightly enough to enable removing the plug.
Then I used a couple of pieces of sheet metal as shims to protect the barrel. That worked fine - I was able to grip enough of the flats near the bolster to hold it firm and the sheet metal protected the barrel from the vice jaws.
The next problem was that the tang is tapered. I don't have any tapered wrenches so I used a crescent wrench very carefully so that the load was taken with the flat of one jaw fully against the flat of the tang, and a piece of sheet metal under the other jaw to keep it from gouging the side of the tang.
In this manner I was able to remove the plug.
In the end, it was highly unnecessary - the breach face was plenty clean and I could see no evidence of any coke build up at the junction.
I wrapped the threads with teflon tape and re-installed the plug, paying close attention to achieve an exact alignment with the top surface of the tang and the top surface of the barrel.
It was an interesting exercise to show that I could do it if I had to, but I think my cleaning regimen, utilizing a breach face scraper is good enough that pulling the breach plug for cleaning is probably not necessary, and it's a whole lot easier to blow things out with CO2 than to pull the plug.
I don't think I'll be pulling the plug again unless it's a crisis.
Steve