Barrel composition of pre 1900 Parkers

[Kensal Rise]

Your barrel questions seem to include a subtle concern for relative safety. As BD has well explained, the composition or name on the barrels (rib) is of more marketing value than insurance against bursting with stout loads.

In all older doubles, the primary concern with barrels should be pits and wall thickness after honing. With barrels that still have relatively safe walls, there is little worry no matter what the name of the steel used may be.