Bore to noise ration

S

Spectre

Staff Alumnus
Um...that should be "ratio"! :D

Has anyone noticed a relationship between the bore diameter and the noise level from rifles? Assuming an equal sized case- say, a .30-06, same-length barrels and equal power loads, will the noise level increase or decrease as one goes from .25 to .27 to .308 to .35? Who here has a similar length .270 and .30-06 to compare, or a .30-06 and a Whelen?

How about a .243 vs .308? I know the load in question will always be a factor as well, but I am trying to find the trend. Is a 6mm louder or quieter than a .257 Roberts which is louder or quieter than a 7x57? Or a .22-250 as compared to a .250-3000 as compared to a .300 Savage?

Your thoughts are appreciated.

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Spectre. I'm not really sure I can answer your question, but I have a .270, 30-04 and 35 Whelan, all with 24 inch barrels. As near as I can tell, they are seem to bark with the same level of loudness. I think you would need a sound meter that registers the noise in decibels to really tell, and then it would be academic as all three are loud enough to cause hearing damage.
Part of the noise factor, I believe, depends on the powder used. For example, for years, I loaded the .308 Win. with H-335. The rifle had a 20 inch barrel. At high noon, on a bright sunny day, you could still see the fireball that erupted from the barrel. The muzzle blast and concussion were something to behold. A change to W-760 made for a more pleasant load with less noise. (Still need ear protection though.)
The longer the barrel, the quieter the gun and the muzzle is farther away from your ears. (Not so with single shot rifles)
The smaller bore (270) does seem to be more of a crack while the larger bore (35) is somewhat more of a boom, but the noise level still seems to be the same to my bad ears. (70 percent loss in the high frequency ranges, mostly due to shooting. We didn't know better back then. Wear hearing protection even with a .22LR.)
Paul B.
 
I think that pressure level and barrel length have more to do with it than bore diameter. A short barrel (20") .308 is one of the noisiest ones around, and I am not speaking of firing it but hearing it go off from a distance away while hunting. This particular rifle was owned by my ex-brother in law's brother and I had another friend that hunted with us that also had one. While in the woods or just "popping a few caps" you certainly knew when these 2 fired their rifles. The .308 is also loaded to a higher pressure level than the 06, 270, and other popular calibers that are used in our group.
 
Thanks. I'm planning a sporter, and wondering if there is a substantial difference between several cartridges based on the same case, from equal-length barrels. Based on this, though, I would think the 6mm Remington (older parent 7x57mm) would have at least a little less noise impulse than the .243. Still wondering how (if?) the equation changes with bore diameter.
 
I agree with Southla1. Take a 20" .30-'06 and a 26" .308 and I think it will prove the point. The powder and bullet used would have an effect too. But that supports the pressure level assertion. I don't know about detecting the difference by ear, though.

Here are some other factors ... shotguns seem to be louder than rifles. If you record a shotgun report and put it up on a spectrum analyzer capable of displaying the audio spread, the audible frequencies that comprise the report of the shotgun are dominant and high in amplitude at the low end (freq). A rifle is dominant at the high end of the audible spectrum. That's why a rifle "cracks" and a shotgun "booms". A shotgun report also seems to last longer, while a rifle report is short and sharp. The lower the dominant audible frequencies, the more natural surroundings, even man made buildings will echo and "resend" the report. The higher frequencies of the muzzle pulse from a modern rifle load can't find as many man-made or natural surfaces to maintain amplitude as it's reflected. Also, higher frequencies die out sooner than lower ones, with distance.

It's not possible to leave everything the same and just change the bore diameter. In the physical design of the cartridge, yes, but in performance, everything changes with it. Pressure will drop with a larger bore, for one thing. It may be quieter, but it would take an audio meter to tell the difference, because your inner hearing will saturate long before the level where the difference is measured. (edited: If you are some distance away and experienced at hearing and identifying sounds like this, you probably could tell the difference. I was thinking of standing next to someone at the range.:))

In other words, I still agree with Southla1, but have you ever tried picking fly poop out of a pile of pepper? They're all loud.:)


[Edited by sensop on 05-26-2001 at 11:01 PM]
 
Spectre, I have to agree with "sensop"...they are all loud :). By hearing alone I cannot tell the difference between the 6MM Rem. or the .243 Win. As I stated I CAN tell a .308! One thing,when you mentioned the parent of the 6MM/244 Rem. It kind of reminded me how sweet shooting and not so loud the parent (7X57) is. that is one sweet round in the original loading and the 95 Mauser. It is loud but cant hold a candle to a .308 :D.
 
Purely subjective, of course....

but the smaller bores seem to have a higher, sharper pitch. The .223 from the M16 was far more unpleasant than the 308 from the M14. Not that I would willingly fire either of them without hearing protection.

The report of the 40mm M79 grenade launcher was nearly pleasant by contrast. Then, one has a much larger bore and somewhat lower pressure.

Shotguns also have a "softer" report. Larger bore, lower pressure.

This sounds like a serious research project. I don't have the equipment for it, but it sounds interesting.
 
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