I got a used FEG (P35 clone, SA) and after putting 200 rds thru I found out the mag or the extractor was causing extract-failures. The mag has been determined to be defective but it could be the extractor is worn too, after shooting rounds individually loaded (mag out) the casing wouldn't extract and eject. The pin above the trigger on the frame walked out while shooting as well. What could cause this?
Let's address them individually.
1. The mag is bad - that seems common on FEGs. The one I got with mine was poor to start with and eventually became unreliable. Others have reported bad mags as well.
2. Don't single feed bullets by dropping in the barrel. That forces the extractor to ride up over the rim. It's not designed to do that. Normally the round feeds from the mag and the rim slides up behind the extractor from underneath. I'm not sure how many times you can single feed it without breaking it, but the number is on the small end of 0 to whatever.
3. The trigger pin is also known to walk on some FEGs. It just needs to be properly staked on each side to keep it in place.
Make sure the follower is in correctly. Mine was in there backwards. Works fine since I changed it around.