Help!! Asking on behalf of my BIL a new Glock 19 owner.What is the break-in period before these become reliable? His new G is jamming badly, with various FMJ ammo brands and with 5 different Glock factory mags. FTFs, FTEs you name it. He is an LEO whose duty gun is a Glock 17 and which he says will only jam seldomly, so I think operator error is out. Maybe 300 rds so far have been fired.