Hmmm... I wonder if I have some of that...
Why is steel cased ammo bad in that gun?
From what I've read, the Glock pistol (maybe depending on which model, the ones chambered for 40 caliber are mostly mentioned) does not fully enclose the cartridge, leaving a bit of the bottom not surrounded by the chamber.
And steel is more brittle then brass.
Steel on steel friction is not good-can wear the chamber. Brass is softer than steel-does not wear the chamber.
Long term use of the Steel cases can damage the gun.
Steel is more brittle than brass and is more like to fail when other factors are out of spec.