Depending on the model, HKs like the old P9S and P7M8 have REAL polygonally 'rifled' barrels. Glocks do not. They just have rounded lands, but they are not true polygonal. That said, there is no issue shooting lead bullets through Glocks. In a real polygonal barrel, you could run into issues, but I don't think you will if you use a hard enough lead alloy.