.........is necessary to damage or burst a shotgun barrel?
Most of us likely know, and believe, that a barrel obstruction, as relates to the possibility of barrel damage, are things such as a lodged sub-gauge shell in a barrel, a lodged wad from a previous (faulty) round, mud, snow ............ in short, anything that completely blocks passage of the next payload. However, I was reading some very interesting things about that this morning and stumbled across an article by Tom Roster, arguably one of the world's top shotgun ballisticians of today. He mentioned in an article in Shotgun Life, in 2014, something I was unaware of ........... that grease or even oil, in the amount of just a heavy coating, can cause extreme pressure spikes. I'm not talking about an amount large enough to obstruct the bore as we might normally consider it, but just a heavy coating in the bore.
This is an excerpt from his article aforementioned. Especially interesting to me was the last paragraph.
"As a gross rule of thumb, obstruction bursts generally take place well down-barrel significantly past the chamber and usually closer in proximity to the muzzle than the chamber itself. The many forms obstructions can take include, but are not limited to, are an incorrect smaller gauge shell accidentally loaded which slips forward of the chamber and wedges in the forcing cone, a blooper load which leaves a wad wedged down-barrel, a plug of snow or mud caused by the muzzle being accidentally pushed into snow cover or soft ground, or excess grease and oil left inside the bore proper which is not properly removed prior to live firing.
A classic example of the first obstruction burst cause is a 20-gauge shell accidentally loaded into a 12-gauge chamber. But this can also occur from a 28-gauge shell accidentally being loaded into a 20- or 16-gauge chamber. Because the 20 gauge, more than any other gauge, can be involved with these two examples of a wrong gauge shell being loaded, U.S. manufacturers wisely elected years ago to color-code all 20-gauge ammunition a basic yellow color.
The oil or grease mentioned above may come as a surprise to even experienced shotgunners. It is a little understood fact in the U.S. that one test European shotgun manufacturers use to fast-proof barrels if standard proofing methodologies and loads are not available, is to liberally oil the bore and then fire a standard service load in it. The well-oiled bore interior will cause the pressure to rise some 6,000 to 7,000 pounds per square inch (PSI) above the Maximum Average Pressure (MAP) for service loads. And grease inside the bore can cause the pressure levels produced by shotshell service loads to easily double."
Likely, not removing heavy bore coatings of oil or grease, before firing, have also contributed to the rivelling and bulges we so often see in barrels.
SRH
