Don’t know for sure as never seen one, but at a guess it might be breech-lock. The 10 o’clock hand-wheel rotates the inner lugged ring of the door, the bolt throw handle then throws the boltwork? That pic is one in Manchester (again!) from what I remember, also had pics of the main rectangular door.
Strange though, as they didn’t use the breech-lock principle on their 1920s cylinder safe. That had a plain tapered plug door with boltwork thrown by the handle, unlike many of the American cannonballs. Quite a few American doors used breech-locks for the small emergency doors though, so you never know. can’t think what else the 10 o’clock handwheel would be for…There’s a few ex-Chubb guys on here so someone might have encountered one of these and be able to tell us more.
