If there were an award for the most colorful, funny, witty, learned, and interesting people on the web, our gang here would win it every year. Thank you for the many helpful responses, and every response has in fact been helpful.
"Good luck in your circuitous search for the most complex solution" wins the blue ribbon, and so thus is this endeavor named after "The Helsley Principle" - Defined as 'the commensurate joy received from deliberately making an already technically difficult project even much more so'.
Der Ami, it is a Lancaster oval bore. This means it shoots bullets that are smaller than than the muzzle diameter, which on this gun is .40825". So I bought a box of .408" 235-grain Hawk bullets and patted myself on the back when at sixty yards they shot perfectly. And then I cried when at 90 yards they scattered like 8-shot. The 230-grain weight of the bullet is in the gun's ledger entry, and the powder charge is engraved on the gun. Unlike conventional rifling systems, the Lancaster oval bore is notoriously finicky, because it operates the opposite. Conventional rifling can handle oversize bullets; bullets that fill the groove are standard. Oval bores shoot undersize bullets. So finding a bullet below the diameter of the muzzle and almost exactly the right weight left me confident of victory. Ha ha. In all the black powder double rifles presently in my care, I now shoot only Swiss and Olde Eynsford FFg and 1.5FG. These two powders shoot so well that they make up for the years of agonizing with GOEX. I like your pliers solution.
I plan to armor up and get out the Dremel. I will report back to you all from the hospital, I am sure.
