When I started with my Knight Disc there was no difference...I always bought CCI 209 primers, because that's what the local mom & pop store had...A few years later, I noticed WalMart carrying the so called black powder 209s...I think I read somewhere that the bp 209s are not as hot as the regular 209s to help with the 777 crud ring...

I don't know if that's true or not, I tried a pound of 777, didn't like it...I never did try the designated bp 209s, still use the CCIs...I'd buy what was cheaper, or more avaliable...If you have a crud ring problem you might want to try the bp 209s...