Magazines seem to be the #1 failure of a firearm.
Normally they cause a failure to feed the next round (not enough spring pressure to put the next round up before the slide closes, or the follower sticking), a stove pipe or a double-feed (new round tipping up and catching on the empty just fired brass, pushing it back into the chamber). There can be other reasons for these issues and this is not necessarily everything a bad magazine can cause.
How to diagnose: First you need to be sure it is a specific magazine and not another factor (dirty weapon, bad ammo, limp wristing et al). Continue reading Firearm Magazine Issues and Diagnostics