Real Avid
Bench-bolted vise with an 8-position ball-and-socket head, rated to 100 ft-lb for serious gunsmithing. The most capable hold on this list for heavy work.
The Real Avid Armorer's Master Vise is built for people who actually build and repair guns rather than just clean them. It bolts to the bench and holds work on an 8-position locking ball-and-socket head, letting you tilt and rotate a receiver or barreled action to the exact angle a job needs and lock it hard. It grips with reversible Gun-Fit padded jaw sleeves and is rated to 100 ft-lb, so it takes the barrel-nut torque and detailed fitting that flex a lighter cradle. To clamp an AR receiver directly you add Real Avid's Smart-Fit lower or Lug-Lok upper vise blocks, sold separately.
The all-steel construction resists the flex that makes lighter vises frustrating under load. At $300 it is the most expensive tool here, and it should be: this is the pick when the vise is a workstation, not a cleaning accessory.
Add the Real Avid Armorer's Master Vise to your build and see how it enhances your platform.