The 'disc' refered to is a small plastic round disc that holds the primer for many Knight muzzle-loaders. I'm sure a picture will follow shortly. Then we have the original 'orange' discs & the newer 'red' discs. It takes a specific bolt & breech plug to handle one or the other. I have 2 Knights that take the orange & 2 that take the red discs. You hear some grumble about using the discs but I don't mind them at all. I have a good supply going forward.
Yes I do reuse them at times. I know the common theme is to only use new ones for hunting, I thought I knew that. Well I loaded some of each for an anterless hunt & got tripped up. The primer was pushed into the disc on the shot. The primer did go off, but at the angle things ended up it failed to light the powder properly. At 1st I thought I had a gun problem, then discovered it was operator error. It was anterless & I tagged out later, but ALWAYS us new discs for hunting. I won't make that mistake again.