I shot my gun today using the thor bullets I had. They sent me a sizing pack and following their simple instruction, found that the size that I got with my gun fit perfectly.
I shot the 250 gr balistic tip using 100gr of 777. Shot great.
On another positive note. I found the people at Thor bullets to be a great help and was surprised to find out when ordering more bullets, that they don't take any money upfront. When you receive the bullets and are happy with the product, they ask you to mail the payment. I find this attitude and basic trust in humanity refreshing and sadly not found in many companies.
For that fact alone, I will use Thor bullets in my muzzleloaders. The fact that they shoot great in my gun is a plus.