The Knight Disc is a great rifle. Your moving down from 150 grains to 100 grains was a good move. Have you tried any of the Barnes 250 grain Expanders? You might also want to try some of the 240 & 300 grain XTP's. They shoot well out of my Knight Disc.

I shoot loose powder. I shoot normally 100-110 grains of 2f Goex and get real good accuracy. I am also shoot some larger heavy projectiles and the rifle seems to like the heavy stuff a lot.

I think a lot of your inaccuracy is because you are not swabbing the barrel free of fowling between each shot. I use a solution of 91% isopropyl alcohol and car windshield washer fluid mixed 50/50. There are other things out thereto swab with also. I run a damp patch is short strokes working from the muzzle to the breech. Then I turn it over and swab the barrel again. I then run two dry patches after the damp patch to make sure the barrel is good and dry before I load the next shot. Remember, swabbing the barrel is much different then cleaning the barrel. I think some people get that confused. Swabbing is just removing the fowling from the previous shot. You do not have to break the rifle down and clean it until the end of the day. (or if you want to test other projectiles I will sometimes break the rifle down for a better cleaning).

To get the best accuracy of your rifle you want to keep each shot as consistant as the one before. That is the reason you swab the barrel between shots.. So each shot is like the other...