An "Oops" Moment at the Range

This weekend, I had headed to a gun range with a friend and my oldest son. Unfortunately, although it was early morning, the longer shooting lanes had already been claimed, and we settled into using a lane that was about 80 yards in length, setting up a steel target (3/8 inch thick) at the far end. After shooting full metal jacket 5.56 and 7.62x39 at the steel target for a while, we decided to try out a .243 my friend had brought with him. I figured that since we had not had any problems with what we had been shooting, and the .243 ammo was Federal 80-grain soft-points intended for hunting, the target would be fine. It wasn't. Now I have a small hole in the center of my steel plate.

So, the issue now is how to fix it. I've a small stick welder, so I suppose that will probably be the easiest (but ugliest) fix. But I was also thinking of drilling the hole out to a standard diameter, threading it, installing a bolt or screw, and then cutting it flush with the surface. Any thoughts would be appreciated.