Ironball! Listen up, junior. I tried to tell ya. There are a couple of people here that think that because they have been here a long time, they can dictate the terms of discussion. Some people here take a "my way or the highway" response to every thread. Looks to me like the big boss man GB doesn't agree. But watch your step, son. Be polite, obey the rules. The good ole boys are showing their true colors.
Personally, I have to agree with the fact that a blank charge of 1 pound of powder in a 1/2 inch thick tube 12 inches long, like you describe, is no problem. The cast iron is purely decorative, the steel liner will handle the charge. Most of the powder will be wasted by being blown out to burn harmlessly in the atmosphere.