Who made the revelation model 400?

If your model 400 is a semi auto shotgun, with a squarish back to the receiver (something like the Browning Auto-5) these were made for Western Auto by Savage/Stevens/Springfield, and should cross reference to the Mdl 745. The e-commerce side of gunpartscorp.com has a schematic for the Savage 745/ 745C, see if that looks like yours. They DO have some parts available if needed.