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. Peak pressure occurred 22mm (.866”) past the leading edge of the obstruction.
OTOH Greener attempted to burst barrels with various obstructions, and the obstructing materials were just ejected out the end of the barrel.
1936 testimony by W.A. King, Parker Gun Co. regarding a barrel burst, likely a 20g shell inserted before a 12g
https://books.google.com/books?id=jU...J&pg=PA802&lpg
The Double Gun & Single Shot Journal Vol 18, Issue 1, Spring 2007 “Finding Out For Myself” series by Sherman Bell described his attempts to burst barrels with various obstructions, including a 20g shell.
Attempts to destroy a Mossberg pump shotgun with 20g shell obstruction
https://www.youtube.com/watch?v=GguN4KyGQCM
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