I bought this at a local gun store for five bucks, I thought it might be a 12 gauge attachment as it fit on the end of mine. Wrong. Maybe. I dont know. The only other guess I would hazard is it's a grenade launcher attachment. If the pics dont do it justice, the construction of this object is about as mil-spec as it comes. This sucker was made to last, forever. Its about 6 inches long. On the big wing nut there is a stamped engraving that says EF. Its smooth bored, and looks certainly like a slip on attachment, where you would then tighten down on the wing nut to secure it in place. Additionally the sights on it do not allow for any windage or elevation changes; so whatever it was launching, shooting, blowing up must have been relatively close. Thats about as descriptive as I can get. Thanks for any info.