I saw one of these back in 2014. There was a member on this board (Fletched Pair) who was helping Donald Dallas with the book on Dicksons. This is his reply on the 28ga MacNaughton's:

"All these 28g Macnaughtons have short barrels like this. They were built 'in the white' as a batch of small calibre double rifles with 24in barrels but at some point the maker built a few as 28g guns when they went out the door."

The blued receiver is odd and the 24" barrels aren't in vogue.

Ken