I'll be darned! Did this thing have "Kruger" molded onto the side panel? This sounds like the very first Luger I owned, probably sometime before I was eight years old. It was black, may have been Bakelite.
I remember the steel barrel insert, but I never knew that it was intended to fire bird shot--all I knew was that you could stack several paper caps into the "chamber" and the breechblock "hammer" was powerful enough to set them off--put quite a respectible flame out of the muzzle at night!
Not only not politically correct, but iirc it was full-sized (or nearly so) and all black--it could probably get you arrested today, or at least get your kid expelled from school.
Thanks for the memory!
--Dwight
As a postscript to my original post, I found this ad for sale on ebay. I also recall one of the actual guns for auction on ebay last year some time.