I agree that glock says no cast bullets. A manufactures warning is not something to be ignored but when you think about it many manufactures say don't shoot reloads at all. Many do shoot cast in their glocks without problems. The individual would need to make decision for themselves.
I personally think glock gets its reputation for leading due to the two most common calibers it's sold in are possibly 9mm and 40 sw. The 9mm is known for having barrel diameters all over the place.leading to folks using.356 when it may be to small to size cast in that particular gun. 40 SW brass is know to have spring back tendency which is known to size down your lead bullets.
I personally think glock gets its reputation for leading due to the two most common calibers it's sold in are possibly 9mm and 40 sw. The 9mm is known for having barrel diameters all over the place.leading to folks using.356 when it may be to small to size cast in that particular gun. 40 SW brass is know to have spring back tendency which is known to size down your lead bullets.