Decibel levels 5.56 vs. 7.62x39

Status
Not open for further replies.
magyars4

magyars4

Member
Joined
Dec 25, 2002
Messages
430
Location
Indiana
Did a search and couldn't find the data...
And...maybe this should be posted in the semi auto handgun section.
All else being equal
Say an AR platform with 10.5" barrel
Would the 5.56/223 around 3000 fps be louder than a 7.62x39 at approx 2200?
Logic tells me that once your above the speed of sound that there would be no significant difference.
 
magyars4 said:
Logic tells me that once your above the speed of sound that there would be no significant difference.
Click to expand...
Sorry, that's faulty logic. Above the speed of sound you still hear the original sound, you just hear that sound PLUS the sound of the supersonic shock wave.

Other than that, I think the difference in the decibel levels you're going to experience will be mostly due to barrel length, so given equal barrel lengths, and all else being equal, I think your conclusion is correct (even if the logic getting there wasn't). I haven't noticed any significant decibel-level difference between my AR's and my AK, but then that's not something I'm focussed on when shooting them, so take it with a grain of salt (or gunpowder, if you prefer).
 
wiscoaster said:
Sorry, that's faulty logic. Above the speed of sound you still hear the original sound, you just hear that sound PLUS the sound of the supersonic shock wave.

Other than that, I think the difference in the decibel levels you're going to experience will be mostly due to barrel length, so given equal barrel lengths, and all else being equal, I think your conclusion is correct (even if the logic getting there wasn't). I haven't noticed any significant decibel-level difference between my AR's and my AK, but then that's not something I'm focussed on when shooting them, so take it with a grain of salt (or gunpowder, if you prefer).
Click to expand...

Faulty logic is one of my attributes...thanks
 
wiscoaster said:
Sorry, that's faulty logic. Above the speed of sound you still hear the original sound, you just hear that sound PLUS the sound of the supersonic shock wave.
Click to expand...
That's not true the two are separate and if one is significantly louder that's what you'll hear.
The supersonic crack of a bullet is a usually a little over 130db and you can hear it if the report isn't much louder like with a 22 rifle. It's especially noticeable shooting suppressed.

As to the OP the report of a gun is dependent mostly on pressure at the muzzle a 5.56 with standard full power ammo is always going to have higher pressure for a given barrel length.
 
mavracer said:
That's not true the two are separate and if one is significantly louder that's what you'll hear..
Click to expand...
I think that's what I intended to mean when I said the "original sound". I didn't mean to say you hear them at precisely the same time. Sorry to not be more clear. But experience says that my hearing, anyway, isn't sharp enough to discriminate. (Must go hand-in-hand with faulty logic). :D
 
wiscoaster said:
I think that's what I intended to mean when I said the "original sound". I didn't mean to say you hear them at precisely the same time. Sorry to not be more clear. But experience says that my hearing, anyway, isn't sharp enough to discriminate. (Must go hand-in-hand with faulty logic). :D
Click to expand...
No worries I learned a lot when I got into suppressors.
The supersonic crack of a 22LR is a lot louder than the report of a suppressed 22LR and knowing what to listen for you can hear the difference unsuppressed even though they are close in DB they are a different pitch.
My subsonic 300bo reloads are much quieter thru the suppressor than factory subs because I shoot them thru a bolt I can use a faster pistol powder that drops pressure off at the muzzle. The factory loads all use much slower powder to keep pressure up longer to run an ARs gas system.
 
My 16 in ak is significantly gentler on the ears than my 16 in ar. Even if I double up earpro with my ar (a2 flash hider) music will be out of tune and everything sounds tinny. The ak has no such issue.
 
magyars4 said:
Logic tells me that once your above the speed of sound that there would be no significant difference.
Click to expand...
Ah, but there are two things 'hidden' in the one.
The decibel level is one, but the sound impulse is another.

The well above supersonic .233 has a pressure impulse far larger than a "just" supersonic round. Recall that the Mach waves generate their own Mach waves as they decelerate through the Mach limit.

This is why a 20" .223 does more hearing damage than a 6" .44mag.
It's also why calling 140 dB cans "hearing safe" is not always accurate. Hearing damage starts in and around 90-110dB. OSHA says that single incidence 140 dB does not require additional remediation (it get really deep on hours of duration in the regulationese).

DukeConnor said:
Not scientific but I always thought AK,s were louder than AR,s.
Click to expand...
That's probably tied to the difference in barrel length, a 20" AR is going to be slightly less impulse than a 16" AKM, from the cube root function of shockwave propagation. That's interpolation on my part, not something measured.
 
CapnMac said:
Ah, but there are two things 'hidden' in the one.
The decibel level is one, but the sound impulse is another.

The well above supersonic .233 has a pressure impulse far larger than a "just" supersonic round. Recall that the Mach waves generate their own Mach waves as they decelerate through the Mach limit.

This is why a 20" .223 does more hearing damage than a 6" .44mag.
It's also why calling 140 dB cans "hearing safe" is not always accurate. Hearing damage starts in and around 90-110dB. OSHA says that single incidence 140 dB does not require additional remediation (it get really deep on hours of duration in the regulationese).


That's probably tied to the difference in barrel length, a 20" AR is going to be slightly less impulse than a 16" AKM, from the cube root function of shockwave propagation. That's interpolation on my part, not something measured.
Click to expand...

Makes sense. Thanks!
 
magyars4 said:
Logic tells me that once your above the speed of sound that there would be no significant difference.
Click to expand...
No. The sonic boom is a very small part of the noise coming off the muzzle of a .224 or .308 bore. Sonic "crack" barely scales with the size of the body creating the wave, so a supersonic .22LR bullet makes about as much sonic boom as your two calibers do.

The vast majority of the noise is the uncorking of some volume of gas (bore volume) at some residual pressure. I don't know that you can rule-of-thumbs your way into ranking the higher pressure/lower pressure 5.56x45 vs. the lower pressure/higher volume 7.62x39.

I am absolutely confident that both are completely deafening in short barrels.
 
Jerry M said:
One thing that matters a great deal is the muzzle device. Is it a flash suppressor or a break? The competition type breaks like the type used in 3-gun are loud as hell. < Not scientific term.
Click to expand...
Agree with this. Muzzle device can really change "perceived" dB vs actual. Where are you measuring the sound from? Ear? Front? At the muzzle? 10ft away on a shooting bench?

How many licks does it take to get to the end of a tootsie pop?
 
JeeperCreeper said:
Agree with this. Muzzle device can really change "perceived" dB vs actual. Where are you measuring the sound from? Ear? Front? At the muzzle? 10ft away on a shooting bench?

How many licks does it take to get to the end of a tootsie pop?
Click to expand...

From the shooters perspective
 
I will say after years of having 14.5” and 16” AR’s fired from over my shoulders in and outdoors in entry stack training that yes, shorter barreled AR’s are eardrum-killers when fired nearby... even with plugs and muffs.

I do think there is a different pitch to the 5.56 report, it seems to me to have a sharper and higher pitched “crack!” than what seems like the lower pitched “boom!” of the 7.62 x39 or 7.62 NATO.... but that’s just my opinion rather than from anything scientific.

Stay safe..
 
7.62x39 has a dull bark while a 5.56 has a yippity yap.

I have a Mini 14 and Romanian sks, both stock barrels and unmuzzled. The mini 14 is much more painful of a concussion IMO. A bit louder, but definitely a sharper noise. I believe its the bore diameter that influences it, at least partially.

Neither hold a cake to the 14" 22-250 stryker pistol though.
 
BigBlue 94 said:
I believe its the bore diameter that influences it, at least partially.
Click to expand...

It's the bore volume. Both cartridges burn similar weights of powder, but the 7.62x39 has a much larger volume for that gas to expand into before the bullet clears the muzzle. So the muzzle pressure is, i believe, much lower for an equivalent length barrel.
 
Status
Not open for further replies.

Similar threads

W
  • Locked
Noise level of a 9mm carbine vs 223 or 7.62x39 w/16in barrel
Replies
9
Views
7K
EdLaver
E
B
  • Locked
Detailed list of 10.5 inch specs for defense .223/5.56 ammo
Replies
0
Views
4K
brycewise
B
7
  • Locked
300 blk vs 7.62x39 for hunting deer or hogs
2
Replies
39
Views
39K
Newtosavage
N
L
  • Locked
Ideal SHTF/TEOTWAWKI AK Caliber: .223 Vs. 7.62x39 Vs. 5.45x39 Vs. .308?
2
Replies
26
Views
4K
000Buck
0
D
  • Locked
How many decibels with big bore hand cannons?
Replies
9
Views
5K
duns
D
Back
Top