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There are a number of different factors that would result in less noise,
- Smaller cartridges – e.g., .22 rimfires instead of bottleneck rifle cartridges like .308 Winchesters (140 dB vs 167 dB)
- Longer barrels as the noise is farther away from your ear and there is less pressure at the muzzle due to more space for the gas to expand. (2 dB going from 14.5" to 20" in one example.)
Subsonic ammunition as bullets that break the sound barrier create a sonic boom, while subsonic ammo does not. (depends on the cartridge)
Single shot actions, semi-autos have moving pieces that make plenty of noise in their own right and they open the action to load the next round and noise comes from that as well.
Barrel attachment: A muzzle brake will increase the perceived noise (some up to 9 dB) and reduce the recoil while a suppressor will reduce the noise the shooter hears.
Some of these make more of a difference than others, with cartridge choice having the biggest impact.
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Additionally to the previous answer, gunpowder quality (including pressing quality, corning, the size of the granules, etc.) is one of the factors affects on louderness and power.
This post was sourced from https://outdoors.stackexchange.com/a/22166. It is licensed under CC BY-SA 4.0.
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