Have you ever heard of bending an Upper receiver?

[stevegun 1]

LRRPF52, your picture made me want to show the ones I made on my Bridgeport. Although I always use the clamshell type your idea is great for those who may not have one yet.

My vise jaws were made from a bit of High Density Poly...... and if you can see the two faint dimples under the 320 SP they are where I put two rare earth magnets in each jaw.

+100 on, clamp on the barrel when working on muzzle devices.