I hit the Dixie site on Brent's advice and the twist on the 12 is around 1/80?. That twist is good for a roundnose solid conical upward of 750gr.
This could be an interesting gun to work with. I just wonder how badly the regulation would be affected withthe heavy slug. The site lists the suggested load as a ball with 80 gr of powder, and I wonder if that is the load the gun is regulated for.

Tom

Carbonation without fermentation is tyranny