Would like information on DR's built with a "Clam Shell Action". I saw one for sale the other day and have never seen one before. The caliber was 470 NE. Can anyone tell me about this type of action?

What are the strong/weak points of this type of action?

Have many DR's have been built with this type of action?

What time period was this action built?

Basically, I would like to know everything I can find out about this type of action?