I've got a Knight Disc as well...First let me say, my personal limit is 150 yards.

I went to a 250 SST a few years back because I wanted a longer range zero...I use 90 grains of Pyrodex R-S and a 250 SST...I'm sighted 2 1/2 high at 100 and 2 1/2 low at 150.

I did some shooting with the Dead Centers, my Knight didn't group the ones I tried, I think they were 260s, anyway, to do much better than the SSTs I think you are going to have to go to the Dead Centers or one of the Barnes all copper boat-tail bullets...I just couldn't justify the price.