Well, finally took it out to the range today and ran 120rd of Monarch Brass 55gr. With the H buffer, it ran smoothly and without a single hiccup. Didn't act or feel overgassed, and accuracy was on par with any other 16" barrel I've used.

I guess next on the list is a decent light, Aimpoint, Centurion C4, and sling. If I ever get around to asking the builder what it is, I'll post it here. Until anything bad happens, though, I'll just keep running it.