Odd cuts in barrel extension. Not 6.5grendel

[TheOTHERmaninblack]

One of the projects I'm working on is a leopard print AR for my daughter (don't judge:p)

Initially, as It's going to be primarily a plinker, I'm going 5.56. Maybe later when the mythical steel 6.5 shows up, I'll convert it.

Anyway, a guy offered me a barrel that has some unusual cuts in the extension that I've never seen. The upper I'm using is an A2 without M4 cuts.



Is this barrel GTG?

Thanks.