Very true on the legal stuff. My intent is not to give legal advice, so perhaps I shouldn't have said anything on that point. We can't really comment on video either, because rules can change at any time and the videos cannot.
We did use a set of feeler gages to verify the bolt gap. We did...
Thanks! I stumbled on the thread and figured I might be able to help with the build. It's nice to see some folks taking on the project. :)
I can't comment on the barrels, though, because I simply don't know what the difference is between them. The barrel I used (and Karl's too) were supplied...
FWIW, my understanding is that legally, bending the flat into shape is what makes it into a gun. Once you get to welding, it's already legally a gun.
It really was a pretty straightforward process. We had a slight bit of filing (really just a tiny bit) to fix alignment on the rear weldment...