I dont know a whole lot about mig but I know enough to say i dont think 120 amps whould quite be enough. We get a 250 amp miller in our shop and I think its only rated for 1/2 but thats in a single pass. If your welding to 1/2 inch you will prolly want to use stick and if your not to great then make a few passes cause that will make it stronger yet. Cause there is a lot of stress on that peice the lock goes in when your backdragging. What you might could do is use a 6011 to make a good root pass then go over that with your little mig. Does that sound about right to everyone?