Where did you get the "Merril" tool? How much?
There is a device called a Lewis lead remover that's been on the market for years and it's in the Brownell's catalog. It's basically a wire screen that fits onto a special cleaning rod. That may be the item that you need for your forcing cone. It's made specifically for cleaning forcing cones and barrels. With the adapters, brushes and all the assorted pieces it's around 25 dollars. They're on the web.