I have a couple of questions about the Super Blackhawk barrel diameters:

1) What is the diameter of the 10.5" Super Blackhawk barrel?

2) What is the diameter (muzzle and next to frame) of a 7.5" Super Blackhawk?

I don't have a 10.5", but I do have two 7.5" Super Blackhawks.

I've had my blued one about 35 years. It measures 0.7695" at the frame and 0.7005" at the muzzle.

I've had my stainless one about 7 years. It measures 0.7705" at the frame, and 0.7029" at the muzzle.

I believe there were straight 10.5" bull and 10.5" tapered barreled guns made. A shout over on the Ruger Forum would get you your answer.