I shoot BH 209 also, if none of the above works, try cleaning between shots, one patch with something like hope's #9 elite both sides, then dry patch, then a light oil patch, I use slip 2000 Lube, it won't react with black powder oir BH 209, then a dry patch. Mine would not get rid of first shot flyiers until I did this. I assume you are cleaning the flash channel with a drill bit ever so many shots.

When I first started shooting BH 209 there were occasional flyiers, mostly when I took the gun out of the safe, the first shot was always off. I don't have a place to shoot a fouling shot before I deer hunt and don't like hunting with a fouled barrel, I also don't like leaving my gun loaded for any length of time with a fouled barrel. I tried many suggestions, I tried popping numerous caps before loading, using alchol and/or Hope's #9 Elite, to remove the oil before loading the first shot of the day. I tried using just Hope's #9 Elite to clean between shots, I tried not cleaning between shots. None of it worked, I always had the first shot of the day with a flyier with an occasional flyier.

Then I got thinking about it as It was always happening after I fully cleaned my gun to put it in the safe, the next time I got it out to shoot I always had the first shot flyier, no matter what I did, with nothing else to try, I tried the above between shot procedure. It worked. The only thing I don't do in the first shot procedure that I do at home, is use a wire brush on the barrel after putting the hope's #9 elite in the bore.

I don't know if this will be of any use to you, or even help you. It will be something to try when everything else failes. Good Luck.