As someone said in a subsequent post, real bullets leaving a muzzle have a ultrasonic component that fireworks and blanks won't. Funny enough, at the range today, the guy in the next bay over had a suppressed AR. That made more of a thump noise than what is typical. Probably wasn't running subsonic either. Signature of that probably looks really different. I have a dog that dislikes gunfire - even at a distance she knows gunfire. Same dog will go out in the yard during a thunderstorm with relatively close strikes and pay them no attention. In the house the dog can tell the difference. A strike a quarter mile away that rattles the house doesn't make her look up. Gunfire that we can tell is quite a distance away and is barely audible gets her attention. Maybe gotta try some experiments with something like a bare condenser mic element into a high rate A to D converter. I've got a Focusrite Scarlett that will do 20Khz, but I'm not sure that's high enough. I have some other stuff that can digitize at a few Mhz that might capture what it really looks like. When I find the time....
