Agreed John

U.T.?
 

Just a thought here guys, but over the years in the bridge building business I've had need to check welds in some pretty precarious places, usually in existing structures that had for some reason become suspect.. In many of those places, positioning a "source" for traditional X-ray examination wasn't feasible or sometimes even possible. In those instances, we've utilized ultrasonic testing. Owners are sometimes hesitant, because a permanent record (X-ray film) is not produced by the process. The process ends when the machine is turned off, but a qualified technician then reports to the owner what they've witnessed during the testing, and that usually will suffice when X-ray testing isn't possible.
In the current context, where defect discovery is primarily for piece of mind of a buyer or potential shooter of a composite barreled gun, seems to me that U.T. might just be the ticket. Transducer configurations vary, and none of the standard ones will accommodate a shotgun barrel with any purpose built precision, but even a perpendicular transducer would work for a specific spot that someone had reservations about.
I'm sure Francis could weigh in here with additional thoughts, and more than likely I've wasted everyone's time with these ramblings, but as stated before I've seen U.T. display weld and even base metal faults where more traditional NDT methods were impractical or impossible.
Food for thought,
John

Thanks John, It's all good input.

I would possibly try Fluorescent Penetrant Inspection. We use this and a skilled inspector can detect even very small defects very accurately. Many aircraft service centers have the ability to do this. I am sure there are other industries as well. Fluorescent is dye penetrant inspection but uses a fluorescent penetrant and a black light to detect cracks. I cannot tell you how this would work on Damascus barrels but in theory it should provide some good results.

Phil

We used to use the fluorescent penetrant for inspecting large graphite blocks. You spray on the penetrant, wait, wipe and then put a "black light" on it. The penetrant collects in the cracks and fluoresces under the light. It worked well