rc10j1 Are you asking about a suppressed or unsuppressed 300 Whisper? You didn't mention a suppressor in your post. Glocsecure's answer was obviously referring to a suppressed AR-15 300 Whisper. A 16" barrel subsonic 300 Whisper without a suppressor is still going to be quite loud and you'll still need hearing protection. Unsuppressed it won't make much difference whether it's a AR-15 or a bolt action. Muzzle blast will be the only noise you notice near the shooters location. Although the bullet is subsonic from the barrel of a 300 Whisper the propellant gases are still supersonic and will produce a supersonic shockwave 20 to 30 decibels above other sounds.
With a sufficiently long barrel and a cartridge with a small case capacity it's possible to get the propellant gas and the bullet subsonic. A 22LR shooting Aguila 60 grain subsonic ammo in 24" or longer barrel will accomplish that. So will some small capacity large bore cartridges in very long barrel rifles. Generally these need to shoot cast lead as the bore friction is too high to use jacked or solids for that application. They still aren't as quiet as a good suppressor but can be shot safely without hearing protection.
My point is that without a suppressor you will not be impressed by how quiet a 300 Whisper rifle is whether it's an AR or bolt action. The muzzle blast can easily be heard at 500+ yards in a quite area. In the US adding a suppressor requires ATF registration including a $200 tax and is not legal at all in some states. There are other threads and other web sites which discuss the legal requirements.
For a suppressed rifle you can get the noise down to the level where the shooter will only notice the action noise and the thump of the bullet on some targets. For a bystander along the trajectory there will still be bullet noise in the form of a hiss or buzz. Bullet noise will be easily noticeable but hard to tell it's direction. The noise of a 1000 fps subsonic bullet is about 40 db below that of a supersonic bullet. That's independent of how well the muzzle blast is suppressed.
Action noise can be significant but the distance it can be heard depends moslty on the background noise level. The range of human hearing (threshold of detection to threshold of pain) is over 100 decibels. Making a rifle shot completely inaudible in a quite environment just doesn't happen. The best suppressors only give around 40 decibels (1 part in 10,000 sound energy). Hearing protectors cannot achieve 40 db because sound goes though the skull and sinuses bypassing muffs or plugs.
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