We modify over 10 key spots on our BLK barrels before finishing/blasting/final fitment. Barsto manufactures the most accurate barrels on the market, so it's no secret why we use them on all of our complete builds.
What you see here is pre and post-blasting. We use a mix of fine and coarse aluminum oxide to get the perfect concoction of matte finish on the valley's of the insets. There is still a lot of work involved even after this stage. The top and right side of the barrel are both polished to a mirror finish, the tape is removed along with the sacrificial case from the chamber, and then the feed-ramp and chamber area are polished by hand.