I'm pretty sure this is the same barrel you sent me pics of in a PM and you included pics of pellets pushed through the barrel. Those pellets sure have the same look that a pellet pushed through my LW polygonal barrel have.
It's hard to tell the pics on my computer screen (its a little blurry) but it kinda looks like a poly barrel. What kind of gun did this barrel come off of?
It may be a polygonal rifled barrel. I haven't looked at many but I do see six flats there. There are several different styles of polygonal rifling I've found just now from searching. Here is one picture that can seem confusing but is polygonal.