The BH is a legendary solar sniper found/awarded in the CE raid. At first glance it appears to be nothing special, having just a 3-shot magazine. Certainly, the 6-shot Icebreaker is better in most situations... except for when you need to have another exotic online.
The BH's claim to fame is the attribute of "3 critical hits return the ammo to the magazine" iirc.. If you can quickly make three headshots in a row, you'll not use any ammo out of the mag and can continue shooting without needing a reload. Tough to do in CE, except for the ogres (or maybe the oversoul... I haven't tried it yet).
However, the Goliath/Spider tanks in the Valus or Sepiks strikes are perfect targets for the BH. Shoot/hit the legs or thrusters, which count as critical hits, and you'll shoot for as long as you have a target. I shot a 20-25 shot string as fast as I could pull the trigger and without reloading last evening at the Valus tank's thrusters. He was down at the end.
Miss a critical shot though, and the 3-shot mag bites you...