I think in extremely thin barrels a split will occur before a chamber failure with or without any obstruction. The payload is in effect an obstruction and pressure behind it can cause a barrel failure. We are talking about very thin barrels or worse barrels which are thinner on one side than the other. Hoop stress only work if there is no difference from one side to another. If one side is .025 and the other is .015 I would expect more failures along the thinner area.
The only chamber failure I have seen was due to reloader error. Gross over charge of powder. The two barrel failures were due to snow/ice or mud. Guns were in duck blind, factory ammo, both guns had end barrel failures with ring bulges. Most likely one was ice in the choke area. Never know for sure.
