Actually, Francis Bannerman purchased Poppell Island, on the Hudson River, and had his Island Castle & Warehouse constructed.
The concrete is said to have been strengthened and reinforced, using surplus ordnance material.
To be fair Bannerman and his competitors generated a lot of interest in collecting military memorabilia and surplus arms.
These dealers have proved to be a real boon to 'gun collecting'. They preserved, documented and cataloged a lot of collectibles.
The 'parts guns', salvage from fires, 'sportered', altered and contrived arms were probably a small part of the operations.
Attachment 120765Attachment 120766Attachment 120767