I have always clamped the receiver in a bench vice. I use a block of wood on either side, and obviously clamp the flat lower surface and the picatinny rail top, with the upper on its side. I have never had an issue with this, although I've never had anything horribly seized, either.
The downside is that you can't have an optic mounted, so if you have a scope that's a pain to remove, and want to swap muzzle devices, this wouldn't work so well.

