This was in reference to Red Dot powder with a pressure of 10,000 psi.
If this is the case, it would seem any barrel failures past 3 inches would be caused by an obstruction.
As mentioned in another thread recently Sir Gerald Burrard has a very extensive section on barrel bursts in his "The Modern Shotgun". To simplify his conclusions with all ordinary powders useful for shotshells, "IF" the burst does not occur in the chamber area it is not a high pressure problem. In fact he gave an approximate measure down the barrel at which if the pressure could be brought up progressively a normal sound barrel could actually contain a closed cell pressure of the complete powder charge. An obstruction of course does not bring up the pressure progressively but creates a spike at the point of obstruction. Other than excessive pressure, which will occur in the chamber area or an obstruction which will be at some point down the barrel, there is a third cause of burst barrels. This is from an internal flaw within the metal itself. The most common occurrence of this is in steel barrels & is the result of a void formed as the steel solidified. In subsequent working of the steel to form a barrel this void is drawn into a long slender void & on rare occasions can end up being entirely within the wall of the barrel, thus invisible. Even rarer it may withstand proof firing. This accounts for those steel barrels we see occasionally with a long slit running longitudinally down the barrel with no sign of the tell-tale ring bulge of an obstruction.
JDW, all of this is in very close agreement with the SS Mag data & the conclusion you drew, with the addition of the occasional flawed barrel. An obstructional burst is indeed far more common & accounts for the vast majority of those bursts which are not in the immediate chamber area.
