For us non-glock people, post the cal, not the gun model. My comments didn't apply here.
light gray/almost white looking residue -- I've seen that also. But also had some actual leading near the muzzle. I've recovered some bullets, PC is white, was HF RED IIRC (40sw). Abrasion of the PC in the barrel may scuff off enough to cause leading. I do see some 'smoke' from rifle shot on sunny day that isn't powder smoke, more like lube smoke.