Drifter, followed by JG, noted something important. I never thought about it considering the hook sizes being used, but it has long been known when tying flies on forged trout-sized hooks that clamping them too tightly in the vise creates a weak spot, leaving the hook vulnerable to breakage. I use an old Thompson A vise, and it can't put that much pressure on the size Rvrfshr jig hooks I put in it, but a heavier duty vise might. Joe, you might want to test a few and see if that is the probable cause.

Sg