feeding problems. Especially if checking out feeding with live ammo, remove the extractor and ejector when cycling the pc. sometimes the extractor is not properly shaped, or the hole for it in the slide is not properly located, or the extractor has been bent enough to create too much friction between it and the cartridge rim. Don't have this stuff be part of the test equation. See to it that the gun and the mags feed the ammo in question, then replace the extractor and ejector.