Mainboy: There is a lot of good info being given to you, but with a hunt looming, I would be concerned about chasing too many rabbit trails. Every time you change a variable, the process starts over on getting that new load dialed in. If I was in your shoes and worried about being short for time, I'd go back to what was working well with the Powerbelts. Shooting 2" groups (@ 100 yards) with open sights is excellent accuracy, since at least half of that group spread is due to using open sights. You likely would have had less then 1" groups had the gun been scoped.
If you did not have problems with hang fires and miss fires when shooting your original groups, then it is 99.5% likely your problem was a dirty breech plug, that was the variable that changed. There were two solutions mentioned in this thread and BOTH are necessary to clean the flash channel. Get a close fitting drill to ream out the flash channel, ALSO get a torch tip cleaner from a welding supply (a fine wire with jagged edges) and clean out the fine hole in the breech plug. When it comes to muzzleloading, a dirty breech plug is the "root of all evil"...or at least 85% of the problem
If you have a fully clean breech plug, and for the next 10-15 shots you get instantaneous ignition, the primer you were using is fine, since it gave you good accuracy as well. If you have a hang fire with a clean breech plug, then start looking for a new 209 primer.
Before shooting your groups with Blackhorn 209, take one fouling shot, as most guns shoot differently on a clean and oiled barrel. After the fouling shot begin shooting your groups. No swabbing is needed between shots with Blackhorn 209, and swabbing may actually affect your accuracy for the worse. If your shooting session goes over say 30 shots or you notice any delay in ignition, remove the breech plug, ream it out with a drill and torch tip cleaner.
After each range session, fully clean the gun, including reaming out the breech plug and cleaning with the torch tip cleaner. Again, shoot one fouling shot before starting to shoot groups, sight in, or to go hunting.
The only problem I have had with Blackhorn 209, and its a serious one, is I had a stainless barrel corrode out that I didn't clean for several months. I called Montana Powders and they did not have a clear answer for me, only that they have seen it happen occasionally. The best indication I have so far of why this occurred is a theory that certain brands of 209 primers chemically react with the powder and start the corrosion process. For that reason I now fully clean the gun after each range session. The reason I bring that up, is possibly after your early range session, the breech plug (if not properly cleaned) built up a bit of scale in storage, and that is what caused your subsequent problems. More then likely however it was a carbon build up.
That's my 2 cents.
