The old circular breechblock has been around for a looooong, long time. The late Frank DeHaas's 'Vault lock' design is somewhat similar.
Please be aware that should you make one of these type of actions, they are a very weak design and should not be used for anything more powerful than a typical Black Powder 'Rook Rifle' cartridge. I would even be reluctant to touch off a 32/20 with a Black Powder load in one.
That's the reason why there were so few made by anyone. They simply weren't up to the job.
Using modern rounds will batter the rear of the action so hard it will soon deform or split.
Harry
