If someone intends to actually train against that type threat then what does it take to simulate it for practice?
A large enclosed area with about 2,500 watts of stereo feeding a dozen speakers. The music level is up so high it's near the same decibel range of gunfire.
A hundred or more volunteers to act as panicky as possible in area probably near capacity for safe load weights on the floor.
NO general lighting and a lot of special effects - strobes, lasers, glitter ball (ok, dated myself) etc. You are getting flashes of light from all directions in a dimly lit area packed with other humans who are all moving in close proximity.
Because of the directional sound output of a flash hider or device plus the intervening walls sound deflection AND the close proximity of humans absorbing the sound waves the ability to hear a gunshot will be limited. The music will "camouflage" the reports you might hear and muzzle flash will also be just another focused burst of light in a room filled with them.
Starting at opposite ends you are standing in the scene with no idea of a "start" - it's random, there can be a delay of up to 30 minutes before the "perp" starts firing. You can't see his weapon and you don't know if he will start shooting or where.
So, there's your training scenario - can't see, can't hear, and when the shooting does start you could be very well knocked down hard. Simulate hitting your head on furniture, the floor, another bystander? Lets use random players with 24" x 2" pvc pipe, too. Hmm?
You better bring your A game it's going to be contact training and you don't get any safety gear. Nada. You train like you fight. HIGH STRESS training aka no armor paint ball.
Once the shooter does start it's a free for all with people deliberately banging up against you while you decide what the problem is - because most of us are never trained and we take two minutes time out thinking what the heck? then slowly start responding.
At that point the rounds that DIDN'T hit an intended target still in free flight are now zipping around you from across the room. Bullets that don't strike a target keep flying in a relatively straight line until they hit something solid enough to become the backstop.
It could be you, another bystander, etc. One NYC shooting they had 3-4 bystanders hit for the few rounds that struck a homeless guy refusing or incapable of understanding orders. NYC is known for high volume police response to a single perp. Same for the nightclub - you get a lot of collateral hits and there is no way of knowing what was intended - or not. The gunman doesn't care.
And it's now YOUR problem as you draw to fire trying to make out a clear line of sight shot with people fleeing back and forth. They will cross both in front of and behind the shooter you are aiming at.
Well Good Luck with that. You can't hit an innocent civilian and it's your lawyers worst nightmare in court. Plus you chose a higher capacity weapon to increase the odds of hitting more innocent bystanders in a blazing gun battle?
Let me suggest a different strategy - when you finally recognize that there is someone shooting (which will be long after they started) exit the building in a responsible manner. IF, and it's a big IF, you come into sight of the shooter you can then decide to do the one thing that might work well - move to contact distance with the firearm and then empty to slidelock.
I'm no fan of that technique in open combat but up close and personal in this situation it has a place. Of course, the problem remains that you aren't targeting another CCW trying to do what can't be done. And you don't know if they might mistake you for the shooter, either.
Add two more role players to the scene. There can and will be armed responders - how do you sort that out?
No, the tactical scenario is NOT solved by a gun centric solution. If anything the gun isn't part of the solution at all, nearly any gun will do. It's how you interact with the factors and then decide on a course of action that resolves YOUR personal safety without endangering others.
It's a lot more complicated than "You need to carry more ammo in the magazine." All that extra ammo is as much a liability wrongly used as a help rightly used.