I pulled the trigger on my MK18 with a surefire suppressor mounted and looked back at Jason, an active duty military police officer, “That’s actually still kind of loud” he exclaimed while replacing his Peltor headset onto his ears. And it was. An AR-15 chambered in 5.56 is never particularly quiet due to a variety of factors. However, if you are considering a suppressor for your AR-15 we should be candid about what it entails and what to look for.
There are three main sound sources made by an AR-15 when a round is discharged; the muzzle blast, the sound of the supersonic slug breaking the sound barrier and the mechanical noise of the weapon cycling after each shot. A suppressor aims to quiet the sound of the muzzle blast by trapping the expanding gasses from the end of the muzzle and allowing them to cool and decelerate in a series of chambers. In this way the decibel level is reduced. However regardless of this the 5.56×45 is a loud round even when suppressed because the round is breaking the sound barrier which creates a sonic boom.
So how quiet can you expect your AR-15 to be with a suppressor? It’s a hard question to answer and depends on barrel length, ammunition and the suppressor being used. In general a 16 inch AR-15 firing standard M193 produces a decibel level of around 167 dB give or take depending on environmental conditions. Averaging out a couple of the leading suppressors in the industry you see an average noise level of around 136 db with a suppressor attached. Which is a significant reduction. For comparisons sake a unsuppressed 22lr rifle typically falls in the 130 dB range.
An AR-15 can be made quieter by firing sub-sonic ammunition however, the AR-15 will not cycle properly. There are several great calibers out there available for the AR-15 platform that allow the use of sub-sonic ammunition along with reliable functioning. Many choose to stick with 5.56×45 for ammo availability, familiarity and commonality among several other weapons that they may own. For the purpose of this article we will primarily concern ourselves with suppressing the AR-15 in 5.56.