Probably small shavings from the rim of the casings; as the rear of the case slides up the breech face and the rim goes under the extractor, sometimes very tiny bits get scraped off. This is perfectly normal, although some guns do it a lot more than others. Scrub them off with your cleaning brush when you clean the weapon, so they don't build-up and become a problem.
If you think it might be ammo-related, try a different brand and see if there is any change (for better or worse).
"That means that no matter how we reform health care, we will keep this promise to the American people: If you like your doctor, you will be able to keep your doctor, period. If you like your health care plan, you'll be able to keep your health care plan, period. No one will take it away, no matter what." – President Obama, AMA speech, June 15, 2009.
see 13:20 - 13:58
Last edited by DJ Niner; 03-28-2011 at 00:09..