I wish we had something more than anecdotal evidence to work with. The killers wouldn't have been able to wear ear plugs as they needed to communicate with each other and be able to listen for anyone approaching by car or otherwise. It would have been very disorienting for the killers if they were not trained or had practice to handle it. Does anyone know if BJM had a membership to practice frequently at the local gun range? Did she own a lot of weapons and go on frequent night hunts with the men? How long had she been a skilled night time hunter with jungle skills? /s
I've had a firearm, of some sort, since I was 18 y/o and have shot many, and own a variety, and according to what type of firearm was used, and the ammo used, they will have differing sounds, for example, a 357 will have a high pitch sound, and a 44 will make a big BOOM sound. The 44 is deafening to shoot outside, but I'd rather hear it and wear headgear. Without headgear a 357 will make your ears ring all day w/o ear protection. A 44 makes your hearing dull, like you've been to a concert and sat in front of the speakers all night. It may be different for others though. I can shoot my 38 w/o headgear outside and it not bother me but I prefer to take care of my hearing. If the shooters had headgear they could have used hand signals it's not that hard especially if you are a hunter and have to be silent in the woods for hours, or are LE, or military. You learn those things. My dog knows hand signals.
However here is an article about gunfire and recognizing gunfire.
Recognizing Gunfire Inside
http://www.activeresponsetraining.net/recognizing-the-sound-of-gunfire
Gunfire inside a building doesn’t sound like gunfire at the shooting range. I’ve participated in numerous active shooter training scenarios where I have been tasked with finding the “shooter” inside a large building. Even when the person playing the role of the shooter is firing full power blank cartridges, it is difficult to locate him inside a school or office building. The shots sound muffled and the direction from which they are being fired is difficult to determine. Sometimes, you won’t be able to hear the shots at all! I remember playing the role of the active shooter for a neighboring police agency’s training scenario. I was firing blanks from an AR-15 rifle in a vacant multi-story office building. The officers trying to find me did not even hear the shots from just one floor below my location!
Even if you have fired a weapon many times, you should recognize that guns fired indoors sound different than guns fired outside. Go visit an indoor shooting range. The muffled sounds that you can hear from outside (or from the front room outside the range) are most similar to the sounds of gunfire inside a building. Learn to recognize them.