I’m running BH209 in my muzzleloader, and after about seven shots it starts getting pretty hard to load. Once the fouling builds up, the bullet/sabot just doesn’t want to seat smoothly anymore. If I’m in the field and it gets to that point I pull the breech plug and run a few patches with Butch’s Bore Shine until they come out clean. I don’t think the exact solvent matters much with BH209; that’s just what I’ve always used and it’s worked fine.
After the hunt or a range session, I break the whole muzzleloader down, clean everything, and re‑lube all the metal before it goes back in the safe. I usually only have one muzzleloader hunt a year, so it ends up sitting for a while afterward.
I also make sure to foul the barrel before the hunt. My rifle throws the clean‑bore shot several inches away from a fouled‑bore shot, so I always sight in and hunt with a fouled barrel. Hunting in AZ/NM, with short seasons and dry weather, I’ve never had any issues leaving a fouled barrel for five days or so during the hunt.