I think double taps are really nicely covered by the team here
Stovepipes are when the spent brass fails to completely exit the ejection port and is trapped by the slide as it moves forward. This can result in the empty brass sticking straight up and pinched in the ejection port, preventing the slide from returning to its fully forward position (that full forward position is called “in battery”). The resulting brass-sticking-up situation looks like a stovepipe, hence the name.
There are multiple causes for stovepipes, but the common ones are
- “limp wristing” - grip and position allows too much movement on the recoil and bleeds off the energy that should operate the slide movement and extraction of the spent shell
- round is under powered - the firing round doesn’t generate enough energy to overcome the recoil spring and the slide doesn’t travel all the way back before returning forward
- recoil spring is too stiff - the spring overpowers the force of the round throwing the slide backwards and the slide doesn’t travel all the way back before returning forwards
- dry or dirty gun - the slide should be oiled where it meets the rails so it slides smoothly forward and back. If there is too little lubrication or a lot of gunk has built up, it creates additional drag on the slide so it doesn’t cycle properly
- extractor issues - the extractor is supposed to pull the used brass out of the chamber and pop it out of the ejection port, but if it’s not working correctly, that may fail
That list is more-or-less in order by likelyhood.
Stovepipes are a malfunction of the FTE (failure to eject) type but are sometimes included as a FTF (failure to feed). In any case, your gun won’t fire in this condition and the offending brass has to be cleared and a round chambered, then the slide must return to battery, before you can make your next shot.
Clearing malfunctions is part of what your instructor should be teaching you, as it can be critical in a self defense situation.