Do not know if your owner's manual addresses this (Uh- you DID read the manual, right?) However, from the topglock website-
Can I shoot lead bullets in my Glock?
Glock barrels use special polygonal rifling not found in most handguns. This rifling is one of the main reasons Glocks are extremely accurate guns. However, the same rifling can cause a high degree of leading when not using jacketed bullets. In other words some lead from the bullet sticks to the inside of the barrel when it is fired. Too much leading can quickly lead to high pressures which can cause the barrel and/or gun to break or even explode. If you choose to shoot lead in your Glock please get an after market barrel.