If you do some searching on the internet you'll find many sites talking about the sound level of firearms. Here's a pretty good
article about this.
Assuming that we are talking about handguns, based on the article above and other information I've found over the years:
- The decibel (dB) levels for handguns is 155 - 165dB (depending on the caliber, ranging from a .25 ACP to a .357) or an average of 158 dB.
- On average, with a suppressor, the dB is only reduced to 110-120 dB at best
- Firing a gun with a pillow, will only reduce the dB by about 30 at best or (using the ranges above) 125-135 dB.
Below is a noise level chart.
So, a non-suppressed handgun is going to be as loud or louder than well, a gunshot, depending on the caliber.
With a suppressor, a handgun is still going to be louder than a trombone, dog barking in your ear or ice cream truck (best case) or siren or rock/pop concert (worst case).
With a pillow it is going to be louder than a siren or rock/pop concert (best case) or a jet engine from 100 yards away (worst case)
View attachment 380209
Additionally, covering a semi-automatic pistol with a pillow has a pretty good probability of jamming the gun resulting in the inability to fire another round until the shooter took the time to un-jam the gun.
Not sure what effect (re: jamming) it would have with a revolver. But I would imagine with a typical revolver with a hammer, part of the pillow could get caught between the hammer and body of the gun making it difficult to fire a second, or more, round(s) until the pillow was removed. A hammerless revolver, I'm not sure about jamming at all. But, it goes back to my first point, trying to silence a gun with a pillow is nothing like you see in movies, it would be very loud.