Armstrong's claim to build a 21-inch gun

How much of Armstrong's claim that it could make guns as large as 21 inches was bluster?

Very little as a claim of construction capability, but whether the completed gun would work well was another question entirely.

Armstrong's claim is accepted as a statement of construction capability if a customer supplied the money. Whether the completed gun would work well is left open. Funding and the ability to manufacture it would therefore establish less than successful practical performance. No more specific performance assessment is offered.