Shouldn't you be asking why?
EVERY GLOCK OWNER SHOULD KNOW THIS!
Originally Posted by Crispy129
Alright, so no lead bullets and I'm good?
Glock uses polygonal rifling. This is a type of rifling where traditional lands and grooves are replaced by "hills and valleys" in a rounded polygonal pattern. (Usually a hexagon or octagon)
Conventional rifling on the left, Polygonal rifling on the right.
Lead bullets and polygonal rifling
The manufacturer Glock advises against using lead bullets (meaning bullets not covered by a copper jacket) in their polygonally rifled barrels, which has led to a widespread belief that polygonal rifling is not compatible with lead bullets. Noted firearms expert and barrel maker, the late Gale McMillan, has also commented that lead bullets and polygonal rifling are not a good mix. However, since neither H&K nor Kahr recommend against lead bullets in their polygonal rifled barrels, it is probable that there is an additional factor involved in Glock's warning. One explanation is that Glock barrels have a fairly sharp transition between the chamber and the rifling, and this area is prone to lead buildup if lead bullets are used. This buildup may result in failures to fully return to battery, allowing the gun to fire with the case not fully supported by the chamber, leading to a potentially dangerous case failure. The other explanation is that Glock's barrels may be more prone than normal to leading, which is the buildup of lead in the bore that happens in nearly all firearms firing high velocity lead bullets. This lead buildup must be cleaned out regularly, or the barrel can become constricted and result in higher than normal pressures.
The .45 caliber Glocks have octagonal rifling vs the hexagonal rifling in the other calibers.
The octagonal rifling provides a better gas seal in the large caliber .45 ACP. Notice how the image on the right has a lot less space between the bullet & barrel compared to the image on the left:
Polygonal rifling is very different from conventional rifling. There are no distinct transitions between the lands and the grooves. The illustration below shows the polygonal rifling in a Glock 9mm LUGER pistol.