This is a second hand story that happened to a friend of mine last week, although this type of thing happens a lot and has happened to me. People where in their shooting stalls and were shooting targets down range. A rather inexperienced and dangerous (because of the inexperience and ignorance) individual was shooting his gun when it jammed. Instead of doing a tap-rack drill, he turned the gun sideways to look at it and proceded to rack the slide. His finger remained in the trigger guard, on the trigger. While doing this, the gun was pointed at my friend's head who was working with another individual. All this happened without his knowledge. Another buddy witnessed the event.
Always be wary of where your gun is pointed, even if it is jammed or out of ammo. The gun should always remained pointed down range. If you don't know what to do with a jam, do not carry the gun with you to seek help. Either leave the gun in place, in this case on the counter of the shooting stall, or raise your hand and ask for help. Of course this last procedure may vary from range to range. Always follow range rules for dealing with problems.
Always be wary of where you gun is pointed. During every class I have taken, I have been 'swept' by someone with their gun. Sometimes it has been unloaded, sometimes not. 99% of the time, the person is focussed on something else, and this is where people get into trouble. I cannot stress this enough. Just like driving a car, distracted people with dangerous machines (guns, cars, flying planes, etc.) become very dangerous people.
There was another thread on the Remmington 700 where some lady was unloading it, had pointed in a safe direction, had a problem and redirected the rifle to get a better grip and it went off, shooting through a horse trailer and killing her son. She was focussed on the problem and not on being safe. Things I have witnessed include being swept by someone searching for a dropped bullet, somebody called their name and they turned around (sweeping all of us), had a jam and were trying to fix it similar to above, had their front sight or rear sight come loose and turned from the firing line in search of a tool - gun still loaded with a round in the chamber and others in the mag, were injured while firing or had hot brass drop down their shirt and in the process of dancing around, pointed at us.
It depends on where you shoot, but we operate on the idea that safety is everyone's business. There is no room for politeness when someone is absent-mindedly pointing a gun at you. If you do not make people aware of their problems, they will continue to make mistakes and for these types of mistakes, someone may get seriously hurt or killed. People don't like to be corrected, but it is better that their egos be hurt than you be dead. And they may not appreciate it, but if you keep them from killing someone by accident, you have saved them a lot of money and possibly jail time.
As an aside, after resetting targets or some lull in firing, it is not a bad idea to verify everyone is wearing their 'ears' before you start shooting. If there is no range master and you wish to start shooting, it is a good idea to call "Range is hot! Eyes and Ears on!" then wait a few seconds before blasting away. Your fellow shooters will appreciate it.