Josh... First off, welcome to the forum !
I shoot the 250gr Gold Dot in my .50 Disc Elite and .50 T/C Omega. I use the Harvester Short Black in the Knight and Harvester Black Crush Rib in the Omega.
Even though both the 250 and 300 Gold Dots are .452 diameter, the 300 has more bearing surface and will probably load tighter. I bet one of the 2 Harvesters above will work for you in the Knight.
Good Luck... Rob