I read where the rifling of the Glock is different that land/grooves. Lead will foul the rifling that’s why Glock developed their own round. What I read ....
The Glock has polygonal rifling. You do not want to shoot cast lead bullets because it will gunk up the barrel & kaboom. You can buy aftermarket barrels with traditional lands and grooves that will shoot reloads.
The reason Glock developed the 45 GAP was so you can have a 45 that pretty much has the exact same grip size as their other popular 9mm & .40 caliber models. The round is just a tad shorter and maybe loaded a bit hotter, but basically shoots just the same as a 45 ACP.