but it can work if you have a vice or something to lock it into.
I don't think so.
Rifles recoiling in machine rests or accuracy cradles launch bullets at a different angle to the line of sight than when they're shoulder fired. There's typically about 1 to 2 MOA difference in windage settings from a shoulder fired rifle sighted in as it rests atop something on a bench compared to sighting it in from standing. Smaller differences exist between artifical rests and standing, kneeling, sitting and prone.