Wow! You guys are going to be tough to keep up with. I can add very little to the excellent information posted in this thread. It's all, pretty much, 'spot-on'.
Lead bullets used in a Glock should be between 12 and 20 BHN. Any softer and they'll shed lead; any harder and gas blow-by (and lead removal) can occur. Powder charges should, also, be kept at mid-range or lower.
You've got to do a little experimenting. If you don't have a Brinell Hardness Tester (copper hammer) you can do a simple fingernail or knife edge test. Try to press your nail or the edge of a knife into the lead bullet. If it dents easily the lead is too soft. Experience is the best teacher.
Until you know what you're doing, you should check your Glock's barrel for excessive leading every 25 rounds, or so. If you discover too much leading something has to be changed either up or down. Lead bullets oversized by .001" are right for most bores. Some of the earlier Glock barrels can handle .002".
I've fired a fair amount of lead in my Glocks. It's all been too hard to easily scratch with a knife blade. Haven't had a problem yet.