Here is a link to one of the oddest guns I have seen come to auction in a while.

https://www.gunbroker.com/item/957655470

I bid on this early because it is unique and aears nicely made.I am a sucker for something like this. However, the price seems to have gone way past anything in that category after the first week.

There is no provenance, no markings, no caliber. It looks like some sort of Martini has been skeletonized and full stocked, with a custom top lever joined to the breechblock. A .700 bore could be a period attempt at the mythical 70-150 winchester. MY guess? I was bidding with the thought that it is a 12 ga bore rifle. An outside guess is that it was based on a Greener Police shotgun. Bore is about right for the original barrel and it could have been rifled to 12 ga depth. It could also be one of the Lancaster series of cartridges.
You might find the action maker on the sideplates under the stock, but I suspect it was completely cut away to make the stock thick enough.

The most intrigueing thing is that I have looked and looked, even at the Hi Def images, and there doesn't appear to be any kind of barrel/action joint visible. Integral unit????

No maker and no manufacturer, alond with no caliber. That's too many unkowns for a wild bid. There is still 5 days to bid.