Just checking to see if any of the old-timers out there might remember a custom barrel Maker with the last name Jacobson.
I recently acquired a model 32 krieghoff and it came with a barrel with his marking on the bottom of the mono block and it is an exceptionally light 29 and a 1/2 inch 12 gauge barrel it weighs 36 oz .732 internal bore but external tube diameter is .055 less than krighoff
I know of a gunsmith who specializes in action job, he goes by the name Teddy Jacobson. I don't know if he's the one you're looking for but i hope that piece of information helps.
