Der Jager,
You are right no sideclips. THe owner told that this was made by the maker himself but this can be wrong. I think that if the maker do it, he decide to ad some engravig later as he used to do with later guns. This is suposed to be his first gun, at least here in Bahia Blanca, as it is numberes "01".
IIRC he made 34 shotguns as O/U and this is the only one I know as a single shot.
I will post some pictures of two more guns made by Sartor. I have do some research as I would like to write an article about his guns for the Doble Gun Journal. Unfortunatelly he pass away a couple of year ago, so I have to get indirect information.
Thanks
Martin