Not an answer to my question, so I will assume you mean active shooters, spree shooters and mass shooters and that you mean actually stopping the shooter in the process of shooting (Mark Wilson, Vic Stacy)and not engaging him after the shooting is over (e.g., Sutherland Springs church). You aren't talking about stopping a convenience store robber type of deal. You aren't talking about those that blatantly failed in their attempts such as Dan McKown (sp?), Byron Wilson (Houston shooting), or Richard White (White Settlement church security guard) because they never got off a shot, McKown because he opted to yell at the shooter instead and Byron Wilson and Richard White were just too slow. You aren't talking about Nick Meli types who pointed their gun, but never fired a shot. The Sutherland Springs church incident also would not really fit because concealed carry had nothing to do with the incident as Stephen Willeford used an AR15 to he got from his safe at home. I assume you aren't talking about incidents where the good guy involved is actually a LEO (e.g. Trolley Springs), though maybe not on duty. Dan Mckown and Byron Wilson were both crippled. Mark Wilson and Richard White were both killed
Interestingly, a lot of the people who do engage active shooters turn out to be off duty cops or people with non-typical firearms training. Nick Meli was an armed security guard. Mark Wilson was a firearms instructor and had previously owned a gun range. Stephen Willleford was a NRA firearms instructor. Jack Wilson who stopped the church shooting in White Settlement was a former reserve deputy (so would have had his LEO creds), head of the church's security team, and long time owner of a firearms training academy.
Vic Stacy seems to be the real outlier in that he had no formal training (not even military), was just a good old boy that like guns, but managed to shoot a gunman who had killed two people and who had a cop pinned down with fire. However, Vic Stacy's situation, like that of Stephen Willeford, isn't a CC situation either. Stacy was in his trailer residence when he heard shooting and exited with a pistol in hand, bypassing a rifle he had at his door for security. I don't even know if Stacy had a CHL, but he didn't need one to have a gun in his residence.
Active shooters, when stopped by normal citizens, often are stopped by citizens using improvised weapons (Giffords shooting in AZ, Loughner beaten over head with folding chairs as he reloaded) or even disarmed by unarmed citizens (Silvia Seegrist disarmed by a lucky guy who thought she was pranking and that it wasn't funny). The Hialeah, FL mass shooter was killed by a citizen using his car to crush the shooter as he pedaled away on his bike
https://www.thehighroad.org/index.p...ns-10-14-03-20-years-later.44786/#post-543457
So out of all that, all I get is Mark Wilson who reportedly had a CHL who actually shot at the gunman, but like Vic Stacy, he responded from his apartment (residence) over the square in Tyler and so having a CHL was not an issue to him being armed.
Mass Ayoob did this article on 10 cases where armed citizens stopped 'active shooters' and it is a bit bizarre...
https://www.personaldefenseworld.co...an-armed-citizen-took-down-an-active-shooter/
Cases 1 and 2, aren't in the US and so not really relevant to the concealed carry issue or mass shootings here in the US.
Case 3, wasn't even an active shooter. Apparently, Ayoob considers a guy with blade weapons to be a shooter. I don't know why.
Case 4, Pearl Mississippi, I don't think in CCW was involved and not shots were fired to stop the shooter, plus the principal had to get a gun from his car, so he wasn't even carrying, so not relevant to the OP query.
Case 5, Clackamas Mall, Nick Meli incident again, no shots fired at the gunman with a jammed gun, so not relevant to OP query
https://www.foxnews.com/us/police-i...ay-gun-jammed-possibly-preventing-more-deaths
Case 6, Jeane Assam, may sort of apply. She was an ex cop working as church security, don't know if she retained LEO creds or had CCW creds, but did shoot and stop gunman
Case 7, church shooting stopped by off duty police officer, so LEO creds, not CCW creds, not your normal Joe Blow citizen
Case 8, Trolley Square, Kenneth Hammond, off duty police officer, again.
Case 9, GOOD example, a doctor stopped an active shooter at a hospital.
Case 10, from 1915, armed citizen stops shooter, GOOD EXAMPLE
So what are we left with? Well, as recently as 2015, Ayoob could not even come up with too many examples without looking outside the US and using incidents where the bad guy didn't even have a gun. Maybe somebody can come up with some better examples, but there are very few examples of non-LEO good guys actually shooting at bad guys who are actively shooting where the good guys were concealed carriers (meaning they were carrying outside of their home when the incident occurred. Mark Wilson, Vic Stacy, and Stephen Willeford all responded from their homes. Many of the responders were not your normal mom and pop CCW types either. They were off duty LEOs, retired LEOs, security guards, and firearms instructors. Two of them, Jeane Assam and Jack Wilson both engaged shooters when acting in the capacity of being security for their churches. Volunteer or paid, they were in place to deal with specific issues.
Where am I going with this rambling? Despite the millions of CCWs out there in America, a bunch of these are stopped by people who are LEOs, retired LEOs, off duty LEOs, firearms instructors, security guards, and/or responding from your home to an event you know to be happening nearby (however, see Another Addendum below)
Addendum - I forgot to mention Joseph Wilcox. He was a CCW person inside Walmart when Jerad and Amanda Miller decided to start their revolution in Las Vegas by killing cops, then going into Wal-mart where Jerad fired a shot and announced the revolution. Wilcox responded to confront Jerad Miller, drawing his gun and passing by Amanda Miller that he didn't realize was involved and she shot and killed him. Wilcox, for whatever reason, never fired a shot. This is another failed CCW attempt to stop an active shooter. Point? Stopping active shooters is dangerous.
Another addendum - here is an article with several instances of shooters stopped by "citizens with guns' although several cases are by cops and several cases are where no shots are fired. It does include instances that I failed to find previously that are relevant. Some of the instances are by people who are responding from home or businesses where no CCW may have been needed to have a gun. Contrary to the article, not all incidents were mass shootings and might not have every become mass shootings, but they were active shootings/shots fired situations.
http://memepoliceman.com/list-of-mass-shootings-stopped-by-armed-civilians/