I think I know what the problem is..
I have 2 Knight disk and never a problem until I started using Black horn 209. All my friends use it and love it. They boast the best accuracy of any powder tried, easy reload, and cleans up fast and easy with Hoppe's #9.(no more water down the barrel- I like that). The one problem it has is that it lights hard. The Mfg. recommends a reg 209 or better yet a mag 209.
I tried it in both knights and had a hang fire ever time.....pop......bang. Then called the mfg tech support, They suggested the problem was primer crud built up in the breach plug. He was right. I used a torch tip cleaner wire to clean the small hole,(bought it at the hardware store) and a drill bit in the large hole that I just spun with my fingers. It took some effort the first try as the crud was hard and didn't want to break loose.... No more hang fires. If I'm at the range, about every 4 shots I stick a paper clip wire in to clean the small hole and at about 15 shots I pull the bolt, then the breach plug, clean out the holes well, skip more anti seize goop, put the plug back in, etc, and back to shooting. 209 has never causes problems removing the plug, but it needs lots of primer fire.
I hope this helps.