A couple of things I would try...Go to loose powder as suggested...My Knight doesn't group well with 100 grs, but does with 90...It makes about a 1-1/2 inch difference at 100 yards...

I clean more than you mentioned...2-3 damp patches with rubbing alcohol and a squirt of Murphy's Oil Soap, put this in a spray bottle and dampen 3 patches and use both sides...Next run a dry patch down and a lightly oiled patch followed by a dry patch....Think about it, when you put your gun away you oil the barrel them probably run a dry patch down to remove excess oil before you load it...You need the barrel conditioned the same way for each shot to have the bullet see the same resistance each time coming out....

Two bullets that group out of 3 Knights that I sight it....The 300 gr Barnes original all copper and the 250 SST with the T/C sabots....

btw...My knight doesn't like the sabots shipped with Hornady SSTs, but did like the T/Cs...It also didn't like SSTs with MMP-24s...That's how picky these things can be, like changing just the primer on a cartridge gun.....

You are on the right track, I would bet if you take a little more time cleaning between shots you will see and improvement and if that doesn't do it, I'd go to loose....