take gun apart look for metal shavings if no metal shavings take toothbrush put t shirt material over it wipe out all the carbon. put grease on the rails the flat area where the lower and the slide come together where the disconnect comes through the frame, oil, yes oil like mobil one you have in your garage everywhere else. both should be applied in as thin a coat as possible where it still covers the entire surface area. you must pull slide all the way back before releasing the slide. oh when i said take it apart i meant firing in, extractor, trigger all need to come out.
try it if it doesn't work
put a round by hand into the extractor (with the slide off the frame obviously) if it has to be pushed in, and when pushed in when you gently move the slide around it stays put, but no scraping when you put it in, or when you ease it out of the extractor)
if it passes that test and doesn't work I got nothing beyond new magazines and polishing feed ramp, or a gunsmith cause your ramp could be too high i suppose or your ejector could be too low blocking the mag from reaching appropriate height