They are Blackhole Weaponry barrels. They recently seem very popular here, there are lots of threads about them. Back before they were marketed by Rainer you could buy Blackhole barrels directly from the manufacturer cheap, I owned 5 of them, they were just over $100. Had bad luck with them, including barrels cut incorrectly that could have resulted in having an illegal SBR, some would not stablize m193 rounds, the bullets would tumble, the full length ones I had from them were severely overgassed. I've noticed others have accuracy problems, others have posted with tumbling bullets, but on the flip side many have posted they were very accurate. The manufacturer does not seem to understand the concepts behind gas port sizing, at one point I was told on the phone by the owner that every gas system, every length had the same port size. Years after that they still introduced 300 blackout builds with a midlength gas system that could not cycle. The manufacturer took care of my issues, and Rainier is a great company if your barrel does not perform I'm sure they will make it right. My lightweight .625 Daniel Defense barrels would outshoot my heavy SS Blackhole ones, so I sold the replacments Blackhole sent me.