Why Warrior's Armstrong breech-loaders struggled

Were HMS Warrior's Armstrong breech-loading rifles simply failures?

Not exactly. Their main difficulty was maintaining new mechanisms and materials in a saltwater environment before the necessary alloy and corrosion knowledge matured.

The Armstrong breech-loaders are not treated as straightforward design failures. The fleet had to learn how to maintain their mechanisms under naval service conditions. Salt water exposed weaknesses in contemporary alloy selection and corrosion protection. A promising weapon can disappoint when the surrounding maintenance system and materials science are not ready for it.