The Graf brass is fine and so is the .284 win brass. If you decided to use the .284 brass be sure to have a good lube on hand like Imperial. they are tough cases and difficult to form. They will come up a bit short until they are fired a few times. If I'm going to load a bit hot, I use .284 brass. For std pressure loads it's the Graf.
I'm not advocationg loading hot for the K31
Also, make it a point to full length resize your brass. Some do fine with neck sizing, but others find they have difficulty chambering. This also applies to COAL. Load to fit your own rifles chamber and not to a recommended OAL be it book or another shooters recipe. With the k31 you can have a slightly oversized case that does not chamber completely. The bolt will seem to have closed and the lock will fall on the firing pin but the pin will be blocked and not hit the primer. Same thing if the oal is a bit too long. The serial numbers on the bolt must be rotated completely to top dead center. If not, your bolt is not closed and the rifle won't fire.
These are wonderful rifles and will serve you well for plinking, match shooting or hunting. My k31s have accounted for a hog and several elk.