I had a similar issue. What I did was to go to Home Depot and purchased some 1/4 bar stock, think it was either 1.5 or 3 inches wide. I cut two of them to about the length of the mag well plus about 2 inches. I drilled a hole in it of the face of the vice on each side. I then placed the mag over the two bars and slowly open the vice and spread the mag apart. Do so slowly as you well have a great deal leverage and you can over do it.