Semi auto feeding problems in a nutshell.
Failure to feed,
1) front mag lips that not slightly wider than rear
2) round already in chamber or squib load
3) not enough freebore in barrel, surprisingly common.
4) case over spec on od
5) weak mag spring or follower wrong angle
6)dirty breech face
7) dirt of debris on round.
8) dirty chamber
9) reloaded amo with bulge near case rim.
10) weak recoil spring
Failure to extract
1) Worn or damaged or dirty extractor or broken/out of spec ejector
2) weak case that over expands in chamber or too hot load does same
3) reloaded amo with over speced od or came from fluted chamber
4)squib load prior (round does not fully feed so extractor cannot grab it)
5) Most frustrating of all is in custom pistol with wrong timing, ejection port wrong shape, too strong a spring, compensator poor timing, obstruction near ejection port
To avoid:
Take down pistol:
1) Do chamber check to see if round freely drops into chamber
2) After take down put barrel without slide into position , insert magazine and manually see if round feeds easily. This can be problem with bullets like heavy truncated cone and common problem in 2011 types. If bullet hits hood without moving forward easily, its a problem of geometry
3) Check extractor by placing round into breech face and see how much force is needed to place in or pull out.
There are other reasons but these are most common
