I reuse the plastic discs multiple times when I am at the range. They do loosen up a bit with repeated use. That can be a good thing because you don't need teh wrench to remove them then. But it can also be a bad thing when humting because you don't want them to slip off or to allow any mositure to get inside and ruin the priming or (worst case) the powder charge.
So - what I do is use NEW disks to hunt with but save the old ones for use while practicing at the range and those I have used 10 or more times.
When I heard that knight was going out of business I bought a new box and began to be more frugal with their use. So now I re-use them a lot more than when I thought there was an endless supply of the disks readily available at the local sportshop!
I would second the motion to what Mike said. I don't have one of these fine rifles, but I have a good friend who does. It's all he uses, and I know that he reuses the discs all the time. He hunts with his muzzle loader in three different states, and so he probably shoots 15 to 20 times a year (he's a good hunter and gets several deer every year). I can't say if he's ever replaced any of these, but I know that reloading them and reusing them is just part of the game for that kind of rifle. They seem to work very well for him.
In the spring of 2007 I was the unfortunate recipient of an injury cause by a damaged carbon arrow that shattered on release of the arrow. I was in the yard going to take a few practice shots before dinner and the second arrow is the one that did the damage. That day will forever be burned in my mind. After I release what happened I made mistake #2 I pulled the tail shaft of the arrow out of my hand causing more damage.
Thank goodness that my wife was home and was able to...