Rocketman is right, there really is no difference between powders--pressure is pressure. However, there is a huge variation in barrel thickness, especially near the breech. Some guns were made for light loads and are quite thin. Others designed for heavy waterfowl have breeches that seem to have been intended for cannon shells. So, barrel thickness and tapers are directly related to what the intended use was. Main caveat is to be wary of using heavy loads in guns that appear to have lightweight barrels. If you don't have enough experience to make a educated judgement about the barrels this is a great time to have a qualified gunsmith to take a look at them for you.
