A friend shot the one-size-fits-all in his CVA a couple years ago. I convinced him to size his bore and order accordingly; his groups were cut in half.
I truly don't understand why people are so averse to using the Thor sizing pack, then ordering the correct size for their muzzleloader. The sizing pack is literally $4, and the process takes about 2 minutes. Is that really too much effort to make your gun shoot well? In the grand scheme of preparing for a hunt, that is nothing.
I also don't understand why people are so concerned with Thor's not being "widely available". Does the UPS truck not come to these folks houses?
Thor's are the best, everything else available is a compromise for hunting in CO.