Should I be shooting lead bullets through a shield 45 with ported barrel??

You certainly can safely for a limited number of shots. BUT, there will be significant buildup of solidified lead in the ports and on the under side of the slide. You WILL have to do considerable cleaning of that residue frequently. Left to accumulate it will cause the handgun to fail to cycle. Unless you are willing to do that sometimes arduous job, you might want to use 'half jacketed' bullets. The half copper jacket will prevent that lead buildup. Of course, full metal jacket bullets do the same job. .....