Chamber pressure and muzzle blast

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Willie Lowman

New member
I recently fired my .44 magnum inside my barn. I had ear muffs on but the blast temporarily deafened me. I had a radio playing and after I shot I couldn't hear the music. Then the sound slowly came back as if someone was slowly turning up the volume.

Got me wondering if there is a relation between chamber pressure and muzzle blast/noise/report?

9mm is listed as having a max pressure of 35000 and 38000 for +p
40 is also 35000
38 special is a lowly 17500 and +p is 20000
357 mag is also surprisingly listed at 35000
357 Sig comes in at 44000
45 ACP is only 21000
And the 44 mag is 36000, also surprisingly.

If these numbers are off, forgive me, I pulled them from google.


I also googled the muzzle blast in decibels for each and they were all listed at 160, give or take a decibel.


But here's the kicker, 357 magnum certainly seems louder to me than my 9mm.

When I fired that 44 mag indoors, even with hearing pro on, I couldn't hear anything for 3 to 5 seconds after the shot. After that I am not going to take my pistol collection into the barn and shoot them all to see if the results are the same.
 
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NoSecondBest

New member
If you were that deaf after firing your 44mag inside a barn, your muffs aren’t doing their job. Seriously. You need to check them and see what they’re rated for. Not all muffs are created equal...not even close to being equal. They range all over the place in their ability to protect your hearing. Get a better set.
 
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NoSecondBest

New member
For indoor shooting you should be using muffs rated for 28-31. If you add plugs under the muffs you can get as much as 36 NRR. You’re not using enough protection. You’re way under protected. I shot for many years without enough protection and now I have a 50% mid-range hearing loss. Your story is very familiar to me. Get some better muffs or end up like me!
 
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ballisticxlr

New member
Just like energy from bullets comes from velocity and projectile weight, sound energy is the product of 2 parts. Pressure does make a big difference but total gas volume still matters because sound travels as an ever expanding sphere so the inverse square law applies.

There is a relationship but it's not quite that simple. To make things that simple we're going to assume that there's an atmosphere and that that atmosphere is constant in density and makeup and that it's roughly 1MM pascals (~10 atmospheres). We're not going to address variable atmospheric properties like density with elevation because it can confuse the hell out of things. If pedants would hold their protestations that would be excellent as this is intended as a simplification for a lay-audience.

Sound has 2 big factors that we measure: Amplitude and Frequency. Frequency I'm pretty sure everyone gets, that's just the pitch of the sound... how many wave crests per unit time. Amplitude can be thought of as the loudness or how high and low the wave crests and troughs go.

Given the caveat above, it's not pressure but pressure differential between the inside of the pressure vessel (barrel) and the outside (atmosphere) and how long it takes for the event to occur. If you're running 1,100,000 Pascals of pressure inside a balloon and instantly release it (for arguments sake, making a single wave crest and trough of pressure) then you'll get a sound of X apparent loudness. If you raise the pressure inside the balloon to 10,000,000,000 Pascals you'll get a sound that's a bit more apparently loud (if I did the math almost 4dB higher which doesn't seem like much which is why I've avoided using dB as a unit of measure. It is mathematically a massively more powerful event). Now we did that with time set as near to zero as could be done without a divide by zero error in the math. If we slow down the release of pressure then the pressure differential inside the balloon gradually is neutralized and so the sound starts loudish but rapidly peters out.

So to finish answering your question: It has to do with how much gas is being dealt with (the size of the powder charge) and how high the pressure was to begin with.

Using your own numbers and some more:

22lr 25000 pressure: Charge weight 1gr
9mm is listed as having a max pressure of 35000 and 38000 for +p: Charge weight 3.5gr
40 is also 35000: Charge weight 4.5gr
38 special is a lowly 17500 and +p is 20000: Charge weight 4gr
357 mag is also surprisingly listed at 35000: Charge weight 12gr
357 Sig comes in at 44000: Charge weight 7gr
45 ACP is only 21000: Charge weight 5gr
And the 44 mag is 36000, also surprisingly: charge weight 24gr
223 rem is 62000: Charge weight 24gr
45cinderblock (my own wildcat) is >62000: charge weight is >15gr

So you'd expect a .40S&W to be marginally louder than a 9mm because both run about the same pressures but there's more charge weight in the 40.

Revolvers are a different beast because of the cylinder gap. That's why you don't see suppressors on revolvers except for oddballs with closing cylinder gaps like the Russian Nagant revolver. A ton of loud stuff exits the sides of a revolver near to where maximum pressures are at (which would be inside the cartridge case and cylinder) before anything happens out the front so revolvers can appear to be extremely loud even for their power level. Put a 9mm revolver and a 9mm semi-auto side by side and I bet you'll say that the revolver is louder.

This is one reason why .223 rem seems so blindingly loud. It is blindingly loud. It's running .44mag size powder charges at very near 3 times the pressure. Put a .44mag Deagle next to an AR pistol (to be fair on barrel length and cylinder gap) and tell us which is louder. It's going to be the one with the higher pressure because they have they same basic charge weight.

If you put a .223rem next to my .45Cinderblock wildcat you'll definitely say that the 223 is louder. I've done this and it is. My .45Cinderblock is loud but nothing like a .223 even though pressures are higher with my .45C, because the gas volume is smaller.
 
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pwc

New member
Sound levels/power doubles every 3 Db.

3Db is half as loud as 6 Db. 10 Db is 3 1/3 times as loud as 5 Db.
 
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P Flados

New member
The point about pressure and gas volume matches up with my understanding of the the sound level.

However, for guns other than revolvers, it is muzzle pressure and not chamber pressure. I will expand on this below. For a revolver, it is a mix. The sound from the cylinder gap is a function of pressure in the gun as the base of the bullet exits the cylinder, and the sound from the muzzle blast is a function of muzzle pressure.

Quickload calculates both chamber pressure and muzzle pressure. Faster burning powders reduce muzzle pressure. I ran 3 loads with just enough powder to push a 240 gr bullet to 1200 fps from a 6" 44 magnum using a 1.61" AOL.
  • H110, chamber pressure 23818 psi, muzzle pressure 6879 psi
  • HS6, chamber pressure 29117 psi, muzzle pressure 5183 psi
  • Universal, chamber pressure 36490 psi, muzzle pressure 4335 psi

FYI, assuming 1" of bullet travel for the bullet to leave the cylinder, all of the above loads have about the same pressure (~22000 psi) pushing gas out of the cylinder gap.

Smaller cases also reduce muzzle pressure. Here is a 44 SP with a shorter AOL (1.3") loaded with the same bullet and to the same velocity. Note that the load below is dangerous and only presented as a theoretical example. As you can see, the chamber pressure went up and the muzzle pressure went down.

  • HS6, chamber pressure 45681 psi, muzzle pressure 3479 psi.

Also, some loads burn 100% of the powder inside the barrel and some do not. For example, a 240 gr JHP 44 magnum with a case full of H110 burns only around 80% of the powder in a 6" barrel. To me, loads that burn less in the barrel (i.e. more outside) seem a lot louder.
 
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Pumpkin

New member
Interesting the 44 special was mentioned. I always thought it was one of the easiest on the ears as far as handgun cartridges are concerned (std loads).
I do think bore diameter factors in somewhat, smaller bores with larger casings really crack compared to bigger bores.
 
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1911_Hardball

New member
Your data excludes powder volume. There's a lot more powder in a .357 than a 9mm.
Pressure is irrelevant. If higher pressure meant more noise .22LR would be louder than .38 Spl or .45 ACP
 
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LeverGunFan

New member
NoSecondBest said:
For indoor shooting you should be using muffs rated for 28-31. If you add plugs under the muffs you can get as much as 36 NRR. You’re not using enough protection. You’re way under protected. I shot for many years without enough protection and now I have a 50% mid-range hearing loss. Your story is very familiar to me. Get some better muffs or end up like me!
Click to expand...

This is excellent advice. The earmuffs used by the OP are rated for a 22dB NRR (noise reduction rating); 25 dB NRR earmuffs would cut the sound pressure level to one half, 28 dB earmuffs would cut the sound pressure level to one quarter, and 31 dB NRR muffs cut the sound pressure level to one eighth as compared to the 22 dB NRR earmuffs. Quite a difference.

One characteristic of electronic earmuffs that is often ignored is their reaction time - how long it takes to detect and block the sound of the firearm. Even though it might seem to be a few milliseconds, that delay does add up over many shots in some level of hearing damage. That's why there are high dollar electronic earmuffs, they have much faster reaction times and do a better job of protecting hearing, particularly for high volume shooters.
 
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JohnKSa

Administrator
ballisticxlr provides good information, however it's less about chamber pressure and more about the pressure at the point that the gasses actually vent from the gun.

For an autopistol, that would be when the bullet leaves the barrel. For a revolver, there's some venting at the cylinder gap and then more when the bullet exits the muzzle.

I recall seeing an article some years ago about a problem with white-tail deer overrunning heavily populated areas on the east coast. Some of the municipalities in question brought in professional hunters to deal with the issue. They were using shotguns, probably to avoid issues with stray bullets, but they wanted to avoid disturbing the residents. At the time there weren't silencers available for shotguns, so the hunters used shotguns with extremely long barrels. That didn't change the chamber pressure, but it did change the pressure at the point that the projectile exited the muzzle, reducing the muzzle blast significantly.

So, pressure--yes. Chamber pressure--no. Gas venting pressure (muzzle pressure?)--yes.

Factors which affect muzzle pressure.

  • Chamber pressure. The amount of pressure you start out with before the projectile starts moving. Chamber pressure is dependent on a number of things in turn.
  • Barrel length. The longer the barrel, the more volume the combustion gases have to fill before the projectile exits.
  • Bore diameter. The larger the bore diameter, the more volume the combustion gases have to fill before the projectile exits.
  • Powder type. Different burning characteristics can keep the pressure higher longer or make it drop faster.
 
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Jim Watson

New member
It would be interesting to have a simulation of chamber pressure vs muzzle pressure vs burnup for Power Pistol. That stuff gives good velocity but has a loud report and bright muzzle flash.


Hearing protection, you can now get 30+ dB NRR, there is no reason to settle for less. The Cool Tactical Group favors Sordin Supreme Pro X which is 19dB. There is an Internet Expert who has fudged the numbers to make it look better, but if you apply his method to a higher NRR set, it comes out a lot better.
 
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stinkeypete

New member
Your muffs are good for hunting, shotgun sports and light use. Very useful.

For indoors, I use the great big giant bulky cans along with in-ear plugs when shooting the big stuff for two reasons-

1. I like hearing things and hope to be shooting many more years and will still like to hear things. Lots of us old sportsmen are paying the price for not knowing about the effects of gunfire in our youth.

2. Protects you from flinch. When muffed and plugged, I feel secure about my ears not hurting so at least that component of fear is removed. There is still the component of holding on to a lit cherry bomb to overcome...
 
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44 AMP

Staff
Muffs have to seal to work properly. Plugs have to fit to work properly. If you wear glasses with earpieces (including shooting glasses) you are negating some of the muff's protection.
 
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rc

New member
Pressure does not have as much to do with muzzle blast as gas volume which from my observations is a direct result of POWDER CHARGE.

A case full of H110 may have the same pressure as less than a case full of w231 but the mass of the powder charge is much less and the blast will also be less.

H110 will produce a much bigger fireball at dusk than w231 because the slower powder also tends to burn less completely in the barrel and a there is a lot more of it left to burn in the air in front of the gun.
 
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