In the process of leafing through eGun, I came across this offering:
http://www.egun.de/market/item.php?id=4314721



The seller evidently does not know what he has to sell, so it was left to the potential buyers to educate him.
The 1920 Krieghoff catalog, of which I have a copy, describes this drilling as the "Self Cocking Drilling KRIEGHOFF=PATENT." The most noteworthy feature of this drilling is the trigger plate lock, which can be removed from the action by turning the lever located in front of the trigger guard, allowing both trigger plate and trigger guard to be lifted out, much in the same way as the triggers and locks are removed from Perazzi shotguns.
This particular drilling is a boxlock. The sideplates' only function is to provide additional space for engraving.
In addition to its removeable lock feature, this action has other notable capabilities. For instance, the same slide which activates the rifle barrel also raises the rear sight and blocks the hammers of the shot locks. Conversely, setting the slide on "shot", lowers the rifle sight and blocks the hammer of the rifle barrel.
A similar feature was available in the NEPTUN sidelock drilling. In addition to the hand detachable sidelocks which were connected with the shot barrels, the trigger plate lock which operated the rifle barrel could be removed in the same manner. Neither of these features was made avaiable in post-World War II production guns.
This particular drilling has suffered the ignominy of having its beautifully grained stock shortened to accomodate the seller's ancestors, whom he describes as a "gnomes", and then very crudely lengthened at a later date.
I will be interested in seeing what price this very unusual gun brings.