Okay, I wasn't going to get my hands on some bore paste, anytime soon so... after giving the bore a good scrub with #9, I took the plunge and tried a recipe of 50/50 vinegar/hydrogen peroxide.

plugged the breach plug and filled the bore. First for about 3 minutes, then agian for about 10 minutes. The longer session stripped the lead off. I had some flash rusting after I drained the barrel, but swabbing again with #9 cleaned that up and everything looked good.