Let me forward this by stating what some of my closer friends here already know - I have 20 years experience as a Glock Armorer and FBI/NYSP certified Firearms Instructor...
A few days ago, I was talking to one of the members of a local organization's safety team. He had purchased a new Glock .40 cal M23. He stated that he had gone shooting and needed some help with sight adjustment. He'd fired 26 rounds of "reloads" and was hitting wide left.
I asked what the reloads were and he stated they were "lead round nose."
I immediately told him not to fire any more and to meet me this morning to get the gun checked out and cleaned.
1. NEVER SHOOT RELOADS FROM A GLOCK. Doing so voids the warranty.
2. NEVER, NEVER, EVER SHOOT LEAD BULLETS THROUGH A GLOCK FACTORY BARREL. Glocks do not have traditional rifling, but a hexagonal profiled bore. Shooting lead bullets causes lead buildup in the bore. That buildup occurs VERY quickly and can cause chamber pressures to increase rapidly to the point of blowing up the gun.
I met my friend this am and inspected his Glock. He had fired a total of 26 rounds of lead round nose bullets through his Glock. The barrel was leaded so badly that I had to use a stainless brush to even begin to see the bore profile. Approximately 1" in front of the chamber, there was a distinct buldged ring in the barrel - rendering the weapon unsafe to fire under any circumstances. If he had fired even one or two more rounds, I am convinced that the weapon would have blown. That little lesson will cost him >$100 to buy a new barrel. At least it didn't cost the gun and damage to his hand or face!
If you own a Glock, DO NOT FIRE LEAD BULLETS through the factory barrel. If you have fired lead bullets, have the gun inspected by a certified armorer or gunsmith, asap...