The general concensus is if the lands and grooves in the weapon are cut, hammer forged or whatever but are not polygonal or swirled lead bullets are ok to use within certain limits based on the lead not working very well at velocities over a thousand feet per second. The feeling is that the polygonal bore weather hexagon, octagon or whatever will build up lead plating making the bore smaller and eventually leading to dangerous pressures. I personally have only put around a hundred thousand rounds through a Glock 21, all cast lead bullets and never had a problem. That said, I do clean my weapon after firing it. Some days I would fire over five hundred rounds before cleaning and the lead was sometimes difficult to remove without a lewis lead remover but it came out and the bore was clean before the gun was put away. I never had a problem with lead bullets in the Glock 21.
