Tungsten is a great material to add to try to manipulate the cg location. It is 2.5 times denser than stainless steel and approximately 4.5 times denser than titanium. However, it only works if the overall shape, size and weight distribution allows it to move that cg enough. The problem with irons like the MP33 or the Titleist 680 irons is that the blade lengths are so short and the hosels are so long that you can not put enough tungsten low and in the toe to make up for the way the dimensional characteristics of the designs distribute the weight. If you did add enough tungsten to move the cg to a good place on those types of designs, the head would be way overweight. It takes a combination of having a good base dimensional characteristic and proper mass distribution within that dimension, and have that occur at a weight that allows for using a heavier material like tungsten to tweak or fine tune the cg location. Tungsten is being used a lot more in an attempt to do just what I describe. Why designers continue to try to use short blade lengths I’ll never know (I actually do know, but that’s another discussion). Truth is, a very slight increase in blade length, hardly noticeable by most, and a shortening of the hosel length would make it so much easier to design more playable blades. If you can do that and enhance with some tungsten in the right places, you can get a much more playable “muscle”.