IIRC several school shootings were terminated by either students or teachers/professors who interdicted with a firearm, which they usually had to retrieve from their automobiles.
The exact details I don't recall.
Several have been stopped by unarmed people as well. I put together the following list as a result of discussion on being unarmed and defenseless in "gun free" zones. Lots of shootings are stopped by unarmed people tackling the shooter as happened recently in AZ with Loughner. He wasn't stopped in a gun free zone, but nobody stopping him had a gun until a late arriving carrier helped keep him pinned down, but never drew his own gun.
http://thefiringline.com/forums/showthread.php?t=436861&highlight=tackle
No doubt that the reason there are so many shooters stopped by unarmed people is that there are so many unarmed people present in the general population, no-gun zone or not. We get less armed citizens stopping mass shootings, in part, because we have less armed citizens than unarmed.
Part of the problem is that those who want to be successful in mass shootings go where others are not armed. I haven't heard of any mass shootings at a gun range, police convention or other event where people are likely to be armed. So, because law abiding people obey the law, the chances of someone preventing a mass shooting are much lower.
Apparently, you haven't looked very hard at mass shootings, locations, etc. There have been several attempted mass shootings at police stations, but either the shooter didn't have many targets or was shot by cops before racking up numbers to qualify the shooting as being "mass." Police stations are often locations of considerable violence and often are places of shootings. The fact that so many people are armed does not stop people from trying to shoot others inside the police stations. And while there haven't been a lot of mass shootings at gun ranges, only an abysmally small portion of the population goes to gun ranges. If you think about it, there haven't been too many mass shootings at Radio Shack stores either despite having more customers than gun ranges and Tandy's employee policy of no guns.
Police station shootings...
Detroit, MI
http://www.youtube.com/watch?v=NsHcQdX9_dc 4 officers injured, gunman killed
McKinney, TX police station shooting
http://newsfeed.time.com/2010/08/17/texas-gunman-launches-assault-on-police-station/
Idaho
http://www.msnbc.msn.com/id/18766089/
See post #73 for more...
http://www.thehighroad.org/showthread.php?t=365954&page=3&highlight=police+station
None at gun ranges. Sure, that may be true, no mass shootings. Then again there aren't that many gun ranges and gun ranges are often located in more remote areas. There are several individual shootings, murder-suicide, and way too many suicides, but no mass shooting/murders that I can find.
It is a bit of a myth that people conduct mass shootings where they don't expect to encounter armed resistence. Generally, there are two types of mass shootings. There are those where the shooting returns to a location where there has been a problem (often their workplace or place where they have had bad experiences) or somewhat random/unrelated locations. In the case of the former, it doesn't matter if the workplace has a policy or not against guns, that is where the problem is and where the shooter expects to take revenge. As it turns out, a tremendous number of businesses have no-guns policies, but the shooter doesn't pick the business location for the shooting because of the policy, but because it is the location where everyone s/he dislikes is located together. The latter seems to be a matter more of convenience and doesn't seem to correlate one way or another with expected resistence.
So when you have a guy that gets fired from the post office, does he drive to a gun unfriendly state and go onto a college campus and start shooting people because he chances for killing more area greater in a gun unfriendly state and at a gun free location with a lot of people? By and large, no, this is not what is done. Pissed off people tend to go back to get retribution from those that have made their lives less than wonderful. For most of these shooters, their goal isn't to kill a lot of people as much as it is to kill a lot of people that caused their problems. This seems more of the norm.
There are exceptions, of course. Charlie Whitman killed strangers, but also family first. Silvia Seegrist went on a shooting spree at a mall where it could be said she had some unpleasant experiences, but she didn't seem to be after anyone in particular. She was mentally incompetent (or whatever the correct terminology is for someone who can't fully understand what they are doing).
John Hinkley is another bizarre example. He definitely went to shoot at a location where he expected there to be armed people and managed to shoot 4 including Reagan before being taken down by folks who were armed, but not by their weapons. And of course, he was insane and his target choice wasn't Reagen specifically, but the President. Apparently he had stalked Carter previously but had failed to act.
When you look at some of the notable instances where armed civilians have stopped shootings, often is the case that they are not typical generic civilians.
Who were the guys who responded with guns at Appalatia State? Students who were police officers. Not only did the retrieve guns from vehicles, but one also retrieved a ballistic vest and cuffs.
That church shooting in Colorado? The person who stopped the shooting was an armed security guard (voluntary, but presence for the purpose of providing protection) who was a former cop.
Tyler Courthouse/Square? Mark Wilson responded and was killed, but apparently wounded the shooter who then fled the scene. Mark Wilson wasn't your normal Texas CHL person. He was a firearms structor who taught self defense and CHL courses and had been an owner of a gun range.
As noted, Trolley Square in Utah was stopped by an off duty officer.
Some, like in the Pearl, MS school shooting, the principal who retrieved a gun from his vehicle was not a cop or firearms instructor.
That is a similar reason you rarely hear of robberies of gun shops when they are open.
Once again, you aren't looking very hard and on top of that, in the grand scheme of retail businesses, gun shops are fairly rare.
http://www.legallyarmed.com/gun_store_shooting.htm
http://www.youtube.com/watch?v=MmlZp822SBE
http://www.liveleak.com/view?i=58a_1180139512
http://www.prnewswire.com/news-rele...nsville-gun-store-armed-robbery-58619372.html
http://articles.baltimoresun.com/1991-12-31/news/1991365039_1_gun-shop-gun-store-troy
http://forums.officer.com/showthrea...ry-of-Gun-Store-(No-Money-Taken-Only-Firearms)