I have since received three examples (paid for by yours truly – I have no affiliation with Green Mountain) and these are my initial impressions.
If you’re used to working with “standard” (26″ long, 1.26″ diameter) barrel blanks, the first thing you notice is how small these are. Unless you were looking for a super-heavy barrel, or a target rifle, however this is good news. There’s a lot less material to remove when profiling the barrel. These are almost ideal for custom AR’s. The blanks I received were wrapped in anti-rust paper, and have a black-oxide(?) coat.
Perhaps irrelevant from a builder’s standpoint, it was interesting to see the material displacement caused by the rifling button that was apparent at the ends of the barrels. (Very hard to photograph clearly).
Inspection with a bore scope revealed surprisingly fine machine marks – a much smoother internal finish than I expected for such a low-cost blank. All in all, I think I’ll be using these pretty frequently.