Ancient history on barrel bursts
https://books.google.com/books?id=inQCAAAAYAAJ&pg=PA91 As Miller said, Greener had trouble bursting a barrel with obstructions
http://books.google.com/books?id=inQCAAAAYAAJ&pg=PA92 BUT a study by the Royal Military College of Science, sponsored by the Birmingham Proof House and the British Association for Shooting and Conservation, showed that an obstruction by 2 fibre wads (total weight of 4 grams) was sufficient to bulge or burst a 12 gauge barrel shooting a 28 gram (slightly less than 1 ounce) load.
Obstructions are no problem...until they are not.
