How to Fill Trim Holes

I did my first batch at age 16 on a 70 swinger using a piece of household copper pipe hammered flat and held on the back side and a wire feed mig, trick was hitting the hole once and moving down the line and just coming back after the first holes began to cool. Don't think you have to fill the hole on your first shot, same with grinding them down. Hit and move, be paitent and it will save you more time when you do start with the filler.