Ironman5,
Don't worry. You would not be the 1st to be confused. There are all sorts of reports about barrels bursting while shooting black powder. The proof houses regularly had barrels burst. It was one of the driving forces behind Damascus development and the search for better fluid steel manufacture.
I am not sure that barrel thickness is the only factor. There were various qualities of Damascus and fluid steel around. Some fluid tubes were dangerous as were some Damascus barrels. I believe the quality of the barrel plays a role.
Measuring thickness and developing safe loads are part of the process. The other is having some one with knowledge to give advice.
Many years ago, I pickup an old Ithaca with Damascus barrels. They looked fine to me. To be sure, I sent them to Oscar Gaddy. When Oscar got the barrels, he gave me a call. He pronouced them unsafe at any pressure. He could see defects in the tubes. With out his sage advice I might be minus a digit or two. He marked the defects and sent them back. We spent some time on the phone so that Oscar could educate me.
Pete
