All the Glock pistols except for .45 caliber have polygonal rifling, the lands and the grooves are rounded, very good for copper jacketed bullets, but presents problems for lead, the surface is very smooth in design, and lead bullets can skate a 1/2" or more before catching and engraving into the lands and grooves, this leaves lead deposits, that can build up quickly depending on the hardness of the bullet and the velocity of the load. I shoot lead in my glocks, but am aware of the problem and inspect the bore often until I come up with a formula for how many bullets must pass, before cleaning thoroughly. Every bullet, caliber, load combination is different, I don't shoot lead at all in the 10mm, as I load them very hot.
Now the .45 caliber Glocks have conventional rifling, square cut lands and grooves, Why? I don't know, but it is usually the most accurate out of the box caliber for a Glock. I have shot thousands of H&G 68, 185 and 200 grain lead hard cast semi wadcutters from this pistol.
If you prefer lead, as I do, I would recommend any of the Glocks in .45acp or .45 GAP. Although I own many calibers, We all know the best start with at least .40 FWIW