Congratulations....
Believe it or not, you are not alone! The problem of late it seems, is that between using borebutter and pyrodex/triple-7 pellets with that particular combination with 209 primer yields a nasty, hard powder residue just in front of the breechplug. I would ditch the pretreated cleaning patches and the borebutter.
Here's what I would try. First off, clean the barrel with a cheap auto brake cleaner from Wal-Mart (be sure and remove the barrel from the gun if you can to protect the stock finish). Then go to the laundry tub, using hot sudsy water....use a mop and pump the water throughout the barrel to remove any of the oil and grease and powder residue, and follow-up rinse with the hottest water you can stand to rinse and dry the bore. Then spray the bore w/Ballistol (a good, water displacing lubricant that has no petroleum products in it) and run through a patch or two to finish.
At the range, I spit-patch between shots. Try it, if you still are having problems with the buildup of the infamous "Crud Ring" try the Triple-7 loose powder....it's allot cheaper. Ultimately, the 209 primers are just too much fire for the combination. Lastly, watch-out for the breech-plug seizing up on you as well! Most don't even tighten the plug down, but leave them finger tight and use anti-seize grease on the threads. Remove the plug after a few shots to be certain it doesn't lock up.
Jim