18" Proof Research - 6mm ARC build and testing - factory and handloaded ammo

[Lemonaid]

Pig_Popper that is some weirdness to be sure. It's hard to picture what could make the throat of that barrel make marks like that, the process of removing the reamer from the spinning barrel would not make parallel marks, a chipped reamer would make a spiral? If you wanted to make a throat that made those marks the only way I can think of to do it would to use a boring bar and make a small cut, back it out and pull it back then make another cut and so forth.
Keep us posted on the mystery!