Feed issues generally come from the improper alignment of the screws. I suggest retrying the whole installation process again, you really have to get those screws down tight.
I have both plastic and metal magazines, they are both identical minus the metal ones have an outer metal shell but the same crappy plastic feeding system. Material composition really shouldn't effect feeding for this situation since the feeding components on both mags are made of the same material.
"Its only a little bit on fire"