I was given a Knight disc in 2005 that was shot twice by my brother (purchased in 2000) I took it apart to clean it and never put it back together until last week, we applied for a muzzle loader elk hunt in NM.  It is 50cal SS green mountain barrel 1/28 twist uses the orange disc which I am converting to the Disc Extreme bolt.  Does anyone know if this is an accurate rifle or anything about them?  After a lot of reading I have settled on BH209 and 290gr Barnes TMZ bullets I know each rifles will have a specific load it shoots best at.  Is this a decent rifle?  Thanks.

Yes, it absolutely is a good rifle!  And the upgrade you did was worth doing. The Green Mountain barrel is a shooter, and Knights warranty is hard to beat!!  Start working up a load now and good luck on your hunt!!

Edit to add...
I like knight rifles so much, I've owned 5, still have 3!!!

Agree.
I have a MK85? that I converted to a Disc 209 and a later Disc rifle, unsure of the actual model number.
Original barrel, and I have found 245-250 gn sabots with about 90 to 100 grains of pyrodex gives the best accuracy - 2" groups at 100 yards - but acceptable accuracy 4" at 100 yards is achievable with many different combinations of bullets and pyrodex charges.  My shots on deer with it have all been inside 50 yards.