Additional reassurance comes from the second phase destructive test in the Birmingham Proof House Trial. The barrels were subjected to increasingly loads until bursting, a bulge of .01, or bore enlargement from .729 to .739.
The following 5 barrels tied for first place in the second phase testing:
English Steel, Siemens - Martin process
Foreign Steel, Siemens - Martin process
English machine-forged 2 rod variegated Damascus
English Superior Barrel Steel
English machine-forged chequered 3 rod Damascus
The five barrels failed at 12.5 times the Definitive Proof load (which generated about 11,000 psi by modern transducers) or 11.34 Drams with 2.82 oz. shot (no attempt was made to estimate that pressure).
It should be noted that the 12th barrel (because of ties) Foreign Pointille Twist failed at 5.77 times DP and the 13th (last) Foreign Four Rod Crolle failed at 5.74 times DP.
