Those inserts certainly reinforce the area of peak pressure, which always occurs in the chamber itself. (Note that Bell's abnormally low pressure readings for 28ga loads, per the above, were taken in front of the chamber rather than in the chamber itself, because he felt the inserts would cause the instrumentation to give pressure readings that would be inaccurate on the low side.) But nothing will guarantee that "flawed" Damascus--or flawed fluid steel, for that matter--won't burst. Although the pressure drops significantly once the shot charge leaves the chamber, the barrel walls are also significantly thinner, even if in the same condition as they came from the factory. Honing, pits, etc can easily result in much thinner spots and potential problems for which the inserts cannot compensate.
