Are the inside of your horseshoe nail holes distorted? If they are, there is a simple tool modification that can help.
I modified one of the first stamps that I ever made into a shaper for nail holes. I learned that if you slightly roll off the lower edges at the bottom you will keep it from marring up the inside of the nail hole.
If you look closely, you’ll see that it’s not a flat edge, so it is not going to cut like a tuned punch. If you put it in a nail hole and you hit it gingerly — just for shaping — you never have to worry about distorting your nail hole because everything is rounded off.
You should always double check and drop a nail, or even go back with a pritchel, but it’s a pretty safe way to shape the nail holes.