Posted by Potatohead: All my markings on the case would be the same. Duh, I did forget, you'll still most likely have ammo left in your gun..but still, they would check bullet and powder..? I didn't figure they would.
Your question was "When people are always talking about not using your reloads for legal reasons, how would they know? As long as all of your brass was the same brand...or am I missing something and about to feel really stupid when someone answers the question?"
The answer was "extra cartridges left in the gun, bullets, powder, primer, markings on the case...".
The markings-toolmarks--on reloaded cases will identify them as such.
The primary reason for the microscopic forensic evidence of cases, primers, and so forth is something different, however. The purpose is to prove that the cases found at the scene were in fact fired in that gun, and that the bullets that stuck or missed the victim were fired from it.
We've drifted off topic, but you did ask.
Let's get back on topic.