Short barrel AR noise levels

[Spartan1980]

I find SBRs in 5.56 just straight up obnoxious unless suppressed and for this reason all my AR pistols are in 9mm.

@GJM I used to shoot a local unsanctioned 3gun match with a guy that ran a NFA'd SBR in .300BO. I would concur with you on the noise level. It's loud but not stupid level loud. That is the only SBR that I would consider using inside the house for defense because just the thought of touching off a 10.5" 5.56 inside the house terrifies me. When I get over my aversion to getting "blessed" I'll pay the tax for a suppressor and build a .300BO pistol for HD. Until then the gage and pistols will have to do.

[HeavyDuty]

I find SBRs in 5.56 just straight up obnoxious unless suppressed and for this reason all my AR pistols are in 9mm.

@GJM I used to shoot a local unsanctioned 3gun match with a guy that ran a NFA'd SBR in .300BO. I would concur with you on the noise level. It's loud but not stupid level loud. That is the only SBR that I would consider using inside the house for defense because just the thought of touching off a 10.5" 5.56 inside the house terrifies me. When I get over my aversion to getting "blessed" I'll pay the tax for a suppressor and build a .300BO pistol for HD. Until then the gage and pistols will have to do.

I intend on seeing how this runs suppressed:

[Paul Blackburn]

Anyone aware of the decibel difference between a 9" 300 BA and a 7.5 556?

[Mark D]

Because they’re fun? Some rifles can just be recreational.

My personal crossover point between a serious and non-serious 5.56 is 11.5”, but I do have a new 10.5” upper I’ll be trying out.

A 5.5” 5.56 is totally impractical and shooting it makes me giggle. I just ordered a .22LR conversion bolt for it so it will have a more practical use, too.

Some people want to look cool on the range, I suppose. On my personal carbines, I don't go with anything in 5.56 sub 11.5", and those are all shot suppressed.

Probably people think they look cool…

My limit is 11.5” in a 5.56mm.

Thanks, I was just curious about the rationale for super short, unsuppressed rifles. They don't appeal to me, but I'm fairly sensitive to noise and blast. I've gotten more sensitive as I've gotten older, which may support the suggestion from @TGS that age has something to do with it.

ETA - I also have some hearing damage (infantry, motorcycles, heavy equipment, etc.), so I'm definitely in the demographic described by @TGS up thread.

[DDTSGM]

Anyone aware of the decibel difference between a 9" 300 BA and a 7.5 556?

I found 10.5 5.56 and 8" 300BO


10.5" SBR 556
No can
162.4
162.6
160.5
162.6
162.6

16" barrel 556
No can
160.4
160.4
160.4
160.4
160.2

300 blk 8" sbr
No can
154.1
153.8
153.8
153.5

ETA: Loudness is measured on a logarithmic scale. This means that an increase of 10 decibels (dB) represents a 10-fold increase in sound intensity and a doubling of the perceived loudness.

From another source (more trustworthy result than the guy who did the above on the range):

The sound pressure level was measured according to Mil-Std 1474D, which specifies A-weighting. Weighting degrades meter performance to match the frequency response of the human ear, and A-weighting is accurate and appropriate only for sound levels below 55 dB. For sound levels above 130 dB, and in particular in the 160+ dB region of the non-suppressed 5.56mm rifle, the measurements should be performed without any weighting (also called “linear” or Z-weighting, depending on the meter manufacturer’s designation). While there is a rough correlation using A-weighting between uncorking pressure and measured sound level, the sound measurements are not considered overly accurate due to compliance with the Mil-Std.

Sound levels are pressure measurements expressed as a logarithmic ratio of the actual pressure referenced to 20 micro-Pascals, the threshold of human hearing. There was a little less consistency in the sound measurements than in actual uncorking barrel pressure measurements, partially because of adding several more variables. These included the acoustic impedance of the air and wind direction/velocity. In addition, the inaccuracies in this sound intensity range by using the called-for A-weighting introduces some level of inaccuracy that would probably not be seen in unweighted measurements. When pressure is plotted against sound pressure level in decibels and sound pressure level is plotted against barrel length, there is slightly more deviation from the projected average, but the trend and general correlation is statistically meaningful. Actual sound pressure levels varied from 162.5 dB(A) in the 24-inch barrel to 165.1 dB(A) in the 5-inch barrel.


https://sadefensejournal.com/barrel-...Dinch%20barrel.

“the only potentially effective noise control method to reduce students’ or instructors’ noise exposure from gunfire is through the use of noise suppressors that can be attached to the end of the gun barrel.” – The Centers for Disease Control and Prevention (CDC)

Research that demonstrates the superiority of silencers over traditional ear protection has been published by Matthew P. Branch, MD. He found, “All suppressors offered significantly greater noise reduction than ear-level protection, usually greater than 50% better. Noise reduction of all ear-level protectors is unable to reduce the impulse pressure below 140 dB for certain common firearms, an international standard for prevention of sensorineural hearing loss . . . Modern muzzle-level suppression is vastly superior to ear-level protection and the only available form of suppression capable of making certain sporting arms safe for hearing.”

https://www.ammunitiontogo.com/lodge...level-testing/

“Noise above 70 dB over a prolonged period of time may start to damage your hearing. Loud noise above 120 dB can cause immediate harm to your ears,” says the Centers for Disease Control and Prevention on its website,

https://hearinghealthfoundation.org/decibel-levels

I know this isn't exactly what you are looking for but I hope it is useful.

I know first hand that being even with the muzzle of a 14.5" 5.56 at a distance of about 3 feet to the right with your left muff cracked causes immediate pain and hearing loss. Went to audiologist a couple days later and got my first hearing aid.

[GJM]

Dan, thanks for this info. Interesting that my "8 inch .300 seems quieter than a 16 inch 5.56" is supported by the data.

[GJM]

As I have more experience (and years) around loud noises, whether they be from aircraft engines or firearms discharging, I am much less tolerant of noise levels that will damage my hearing. I am not sure how much of that is physical tolerance and how much is a desire to protect my hearing.

[HeavyDuty]

I know first hand that being even with the muzzle of a 14.5" 5.56 at a distance of about 3 feet to the right with your left muff cracked causes immediate pain and hearing loss. Went to audiologist a couple days later and got my first hearing aid.

That is terrifying.

I sometimes get looks from the bucks for inserting foamies and muffing up well clear of the range. Youth is wasted on the young.

[TGS]

That is terrifying.

I sometimes get looks from the bucks for inserting foamies and muffing up well clear of the range. Youth is wasted on the young.

If I'm at an outdoor range, I usually insert the foamies while still in my vehicle and throw on the muffs while getting my stuff from the hatch before walking up to the benches.

@GJM To be clear, my intention was never to doubt that gunshots without hearing protection is painful and dangerous. I don't think I'm cavalier about hearing protection, either, given I've been doubling up for years and actually put thought and basic research into the specific earplugs I chose to buy in bulk, and have talked to 3 different industrial safety officers gathering their thoughts on hearing protection issues.

When doubled up, however, they all sound like muffled pops. I can't tell a difference in loudness from one 5.56 to another while doubled up on ear pro, and I certainly for sure as shit cannot tell a difference in loudness between a 1200fps 9mm load and 1400fps 9mm load. I have never been down range of a 7.5" 5.56, but I've been downrange of 5.56 automatics in 10", 14", and 20" barrels (without a berm separating us) for literally tens of thousands of rounds and can't tell a difference in loudness through my ear pro from one to the other. The concussion of an SBR is certainly something of note, but loudness...no difference, no ear pain or discomfort ever noted.

[HeavyDuty]

If I'm at an outdoor range, I usually insert the foamies while still in my vehicle and throw on the muffs while getting my stuff from the hatch before walking up to the benches.

@GJM To be clear, my intention was never to doubt that gunshots without hearing protection is painful and dangerous. I don't think I'm cavalier about hearing protection, either, given I've been doubling up for years and actually put thought and basic research into the specific earplugs I chose to buy in bulk, and have talked to 3 different industrial safety officers gathering their thoughts on hearing protection issues.

When doubled up, however, they all sound like muffled pops. I can't tell a difference in loudness from one 5.56 to another while doubled up on ear pro, and I certainly for sure as shit cannot tell a difference in loudness between a 1200fps 9mm load and 1400fps 9mm load. I have never been down range of a 7.5" 5.56, but I've been downrange of 5.56 automatics in 10", 14", and 20" barrels (without a berm separating us) for literally tens of thousands of rounds and can't tell a difference in loudness through my ear pro from one to the other. The concussion of an SBR is certainly something of note, but loudness...no difference, no ear pain or discomfort ever noted.

If you ever care to share specific earplug information…

I agree - I don’t hear volume differences, but I definitely feel concussion differences.