Muzzle blast

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1899

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In your opinion what is the most significant factor in muzzle blast? Let's not bring barrel length into it - although I know it is very important too.

Is it pressure?

Charge/type of powder?

Velocity?

For example, if you had a load with 50gr of powder and 2700fps muzzle velocity with 50,000psi and a 2nd load with 60gr of powder with the same velocity and pressure, would there be an appreciable difference in muzzle blast?

What if the charges were similar but the pressure was, say 50,000 vs 58,000?
 
Well I would say barrel length or the worst combo short barrels with a brake. Ugh.

However I have noticed that slow and heavy seems abit quieter than fast and heavy.
 
Ok - here is an example from Hodgdon's load data:

.300 WSM 165gr Nosler Partition

Superformance 65gr 2987fps 47,800psi
Varget 57.5gr 2987fps 63,700psi

What do you think? Big difference? No difference? No appreciable difference?
 
Long barrels are much better than short barrels. Going from 26 to 18 inches nets you double the percieved volume and about 10 times the sound pressure levels. Not pleasant or good for ears. The UK's only smart move was allowing sound moderators.

Holding bbl lenght constant, the energy of the shot is likely the culprit. I dunno.
 
philthygeezer said:
Long barrels are much better than short barrels. Going from 26 to 18 inches nets you double the percieved volume and about 10 times the sound pressure levels. Not pleasant or good for ears. The UK's only smart move was allowing sound moderators.

Holding bbl lenght constant, the energy of the shot is likely the culprit. I dunno.
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Yes, I am familiar with the effect of shortening the barrel - but let's say you have a carbine with a 20" barrel. Will it help to adjust your loading technique? Or is the difference between loads like the one I listed insignificant? The difference between those two loads is 15,900psi (33%) but with the same muzzle velocity.
 
Slow burning powders are Super Awesome!

Slow burning powders are killers:
I load 270WSM 165gr VLD with 66gr Retumbo and my 24" rifle really blasts!

To find the root of the problem, I did a very interesting experiment:
I loaded 243 Win 105gr A-Max at around 2800fps
  1. Varget (light recoil and blast)
  2. H4831 (big blast)
  3. and Retumbo (almost awesome).

You could easily tell which powder was used from the muzzle blast of my 22" 243 Win rifle!
Retumbo was easily crowned King of all Blasters ;)

Years ago, I was a rabid 357 Mag revolver shooter and remember very well how a 357 Mag full load of slow burning Winchester 296 powder would scare the hell out of "lesser" 9mm and 45ACP shooters ;)

Alex
 
However I have noticed that slow and heavy seems abit quieter than fast and heavy.
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That likely has more to do with the frequency mix than anything else. We tend to perceive low frequency sound as being quieter.


Going from 26 to 18 inches nets you double the percieved volume and about 10 times the sound pressure levels. Not pleasant or good for ears.
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A change of 10 times the SPL equates to 10 dB and I can assure you that a few extra inches of barrel will not make that much difference in the SPL. It might add up to a couple of dB but that would be about it.

One also has to consider that the limit for hearing damage from impulse sound is 140 dB. Most large rifle cartridges will produce an SPL in the 163 - 167 dB range. Seeing as we are already 20+ dB inside the hearing damage range do we really think that an extra dB or two is going to make the difference?


Will it help to adjust your loading technique? Or is the difference between loads like the one I listed insignificant?
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I highly doubt it. Powder choice and charge weight can affect sound level but the difference won't be huge. If we were to stick with a given cartridge at a constant velocity, the SPL range over which that cartridge operates is fairly narrow, only a few dB or so at most.

By far the biggest factor will be barrel length.
 
Suputin - doesn't the pressure make a bigger difference? I thought the displacement of air molecules, which I assume would be faster/greater with the much higher pressure would make a big difference. Of course not proportional to the increase in pressure, but perhaps notable? You point out barrel length - so let's say you drop from 24" to 18". Your ears will be more than that distance from the muzzle, but for ease of calculation, the longer barrel's muzzle is 33% further, which is equal to the difference in pressure of the two above noted loads. With my weak knowledge on the matter I would have guessed that starting off with less pressure coming out of the barrel would make up for the muzzle being closer to your ears.

Is it the expansion within the barrel - or better put the continued rate of expansion after the bullet leaves the barrel the issue here? ie- the expansion of the gases have peaked in the longer barrel?

Could you explain the physics of why barrel length is so significant?
 
I am not a physicist or a ballistician. My area of expertise is limited to sound suppressors. Out of necessity I have some familiarity with the sound testing of firearms and some of the factors involved therein. When I need to know the technical aspects, I have a couple of experts that I consult with.

Having said that I think that the pressure at the muzzle is very different from the pressure in the chamber which is what we are all more familiar with. Sound is simply a high pressure wave that propagates through the atmosphere. How that pressure wave changes to produce one noise that is louder than another is a mystery to me.

I know that frequency and duration are factors. But I also know that a 14" barreled .223 can be as loud or louder than a 22" .308. Why? I don't know but I have seen the sound data enough times to know that it happens. In fact most centrefire rifle cartridges, regardless of size will meter between 163 and 167 dB. Only the really big stuff like 338 Lapua and 50 BMG will approach or exceed 170 dB.
 
Is it the short barrel of a carbine that seems to make it loud and have increased muzzle blast, or the proximity of the muzzle to ones ears?

Take two 30/06's shooting the same load.
One, a bolt action carbine with an 18" barrell, oal 38".
One, a single shot with a 22" barrell, oal 38".

Will they exibit the same amount of percieved noise and blast?
Will one actually be louder than the other?
 
The General Gas Equation gives you more pressure for less volume, so the shorter barrel will have gas exiting at a higher pressure, and possibly more powder burning outside the barrel. So it is likely to be louder. If the muzzle is closer to your ear that would be louder too.
 
Suputin said:
That likely has more to do with the frequency mix than anything else. We tend to perceive low frequency sound as being quieter.


A change of 10 times the SPL equates to 10 dB and I can assure you that a few extra inches of barrel will not make that much difference in the SPL. It might add up to a couple of dB but that would be about it.

One also has to consider that the limit for hearing damage from impulse sound is 140 dB. Most large rifle cartridges will produce an SPL in the 163 - 167 dB range. Seeing as we are already 20+ dB inside the hearing damage range do we really think that an extra dB or two is going to make the difference?




I highly doubt it. Powder choice and charge weight can affect sound level but the difference won't be huge. If we were to stick with a given cartridge at a constant velocity, the SPL range over which that cartridge operates is fairly narrow, only a few dB or so at most.

By far the biggest factor will be barrel length.
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http://www.rdth.org/publicHearing20...e Sound Data & Explanation for HPB 070417.pdf

28 to 18 inches on a 12 gauge is 10 db or ten times the power to your ears. 26 to 18 on a rifle is ?

Six decibels is significantly louder and four times the power to your ears.

We haven't got past the complication of whether these measurements are at the muzzle or at your ears - Moose Masher points that one out.
 
Noise simply results from pressure (which creates the frequency of the sound) and volume (which creates the amplitude or "magnitude" of the sound). The lower the pressure at the muzzle, the lower the noise level. Volume of gas has an effect as well, so at the same muzzle pressures, a greater volume of gas will produce more noise (e.g. 458 Win Mag over 223, and 300 RUM over 308) than a lesser volume of gas even at the same pressure. Stand between a cannon and a rifle, and even though the cannon has a much lower muzzle pressure, it will be much louder.

As for muzzle pressure, the higher the pressure at the chamber, the higher the pressure will be at the muzzle, and vice-versa. The longer the barrel, the more the gas will have expanded when the bullet exits the muzzle, the lower the noise level, and vice-versa.

Quickload estimates pressure at the muzzle - look at some charts for different chamber pressures and barrel lengths and you'll see what I mean.
 
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I'm no expert but I've noticed a few things. For example take the 35 whelen with 225s 30-06 with 180s 270 with 140s and 25-06 with 90 grainers the 25 seems the loudest and sharpest whereas the 35 is loud but lower thump. I would assume as they are the same case that the bore diameter has a notable effect as well. Again this is just an observation from shooting and standing by while my buddies fire away with these rifles
 
The muzzle being closer to your ears will obviously make a difference but the barrel being shorter also makes a difference.

We use a "reference" position when sound testing firearms and that is one meter to the left of the muzzle. We find that shorter barrels meter louder than longer barrels from the same reference position.
 
A long time ago I read an amazing article called ".308 just as loud as a .300 Win. Mag.?". I don't remember who wrote it, but it went into great detail on all factors involving muzzle blasts, and also the noise that escapes through the action as pressure releases through bolt guides and sleeves and such, even though you wouldn't notice the difference between the 2.
 
A long time ago I read an amazing article called ".308 just as loud as a .300 Win. Mag.?". I don't remember who wrote it, but it went into great detail on all factors involving muzzle blasts, and also the noise that escapes through the action as pressure releases through bolt guides and sleeves and such, even though you wouldn't notice the difference between the 2.
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That is correct, they would meter within a couple dB of each other and at 26 dB over the limit for hearing damage you likely wouldn't notice much difference.
 
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