I'm not sure I have the clam shelll concept down. Is it the round moulding that is below the watertable line on the outside of the action or is ith the long skinny part on the bottom of the barrel that rest on the water table?

The clips look to me to not only be little knives to cut and slash but great directionals to vent gas from a ruptured cartridge or primer in directions to cause pain and injury.

Now what about lumps and monoblocks.

Monoblock would seem to me to be a block into which the barrels were fitted, Can't recall seeing a mono block being used in a Double.