Every gun manufacturer will tell you not to shoot reloads. I suspect that it is a lawyer thing.
Think about this - - -> how many billions of dollars worth of reloading components are sold every year. All the powder manufacturers sell reloading manuals. So do bullet manufacturers.
Heck . . . ask WES what he thinks about reloading.
What you possibly could be referring to is this. Some people shoot several hundred soft lead bullets thru their Glock. The bbl leads up. Then without cleaning they attempt to shoot a somewhat hot jacketed load thru the gun. The bullet tries to squeeze down the bbl with all that lead buildup. KA-BLEWIE !!
I have shot tons of lead thru Glocks. I go to the range with lead and jacketed. I shoot the jacketed first,lightly clean,then HARDCAST lead. If for some reason I deceide to shoot the hardcast first,before I shoot the jacketed I thoroughly clean. No soft lead has ever been shot out on any one of my Glocks.
The Glocks "unsupported" chamber. - - -> The chamber will not have any problems if the ammo that it is fed is SAAMI spec ammo. You can also resize ammo from a Glock bbl. It will not have the longivity of other brass though. I have reloaded some brass 8 times. I figure that I have gotten my moneys worth.
A Glock that does not feed,extract/eject,or fire properly - - -> It is not stock !! The Glock guru's will tell you . . "return everything to stock and problem solved". This is true,everytime. We like to tinker with our Glocks. I know I do. Springs,connectors,triggers,titanium this and that,etc,etc. Pretty soon . . . the damn gun doesn't shoot. It shot out of the box. Now it wont. Guess what ?? You screwed it up.
I do not change parts in my Glocks. (except sights) But I do polish up everything extremely well.
I only own Glocks that are Gen 2 or 3 (+ a Glock 42). I shoot hardcast lead. I shoot high pressure loads . . . especially in my Glock 20,6" hunter.
I understand Glocks,that's why I own Glocks. --- SAWMAN