Muzzle pressure and decibel level?

[andym79]

Hi guys, bit of a strange question, but is there an approximate way of calculating the decibel level from a rifle (I know you can buy meters).

Does anyone have any ideas I know for example that a 25-20 at 1500fps is a lot quieter than a .243 at 3600fps but by how much?

 

[rcmodel]

No idea if there is a sliding scale.

But I'm here to tell you there is a remarkable difference between a 25-20 burning 12.0 grains of powder at 28,000 CUP.

As opposed to a .243 burning 50.0C grains of powder at 52,000 CUP!!!

Oh Yea, there is a difference, you betcha!!!!!!

Without hearing protection??

One can make your ears ring.
The other can make your ears bleed!

A good rule of thumb is 4x the powder, at 2x the pressure is about 8x the 'Crack' when it goes off in front of your face.

But that's just a WAG.

rc

 

[andym79]

One of the reasons I ask is here in Australia, each time you want to add a rifle to your collection, you need to submit a form (permit to acquire) and write a letter explaining how you justify your need for another centre-fire rifle.

I have rifles that are suitable for hunting on large properties, but want to get one that will allow me to hunt critters on much smaller properties. As I have a weakness for levers I have settle on building a new 25-20 using an un-barreled 1892 action.

I will be explaining that it is better suited to use of smaller properties that more common cartridges like the 223, 22-250 and 243 because it is quieter and because if by some chance a shot should be missed that the projectile will travel a lot less distance than typical modern varmint busters!

I can quantify bullet drop quite easily, but I would like to be able in some way to quantify sound level as well. The reason being to my knowledge, most of the people who stamp the forms don't know the difference between a 375 Winchester and a 375 Cheytac (I know that from experience when my big bore permit got held up!).

 

[rcmodel]

I think you are going about it all wrong.

A high velocity light bullet as normally used in varmint hunting will completely explode on impact with the soft target, or the ground, if you miss.

That's why the .22 Hornet, 22-250, .220 Swift, and others were invented for hunting ground-hogs and other small varmints here in the heavily populated eastern USA almost 100 years ago.

For instance, I would be more comfortable having a 70 grain .243 bullet hit the ground at 3,500 FPS in front off me a couple hundred yards away then a 75 grain 25-20 bullet going 1,900 FPS.

I can be assured the .243 bullet will completely, totally blow up on ground contact.

While the slower 25-20 bullet, in a deformed state, will likely survive and skip off cross country right at me!'



BTW: 92 Lever-action?
.218 Bee!!

46 grain FP, going 2,700 FPS at 40,000 CUP.

And only using about 14.0 grains of powder!!

Noise is reasonable, velocity & bullet weight is sufficient to prevent zinging the missed shots cross-country.

What's not to like??
(Except brass is hard to get lately.)

rc

 

[andym79]

There is always more than one way of looking at something. I had not really considered that! However, the 223, 22-250 and 243 will probably travel twice as far before hitting the ground!

I was looking at direct hits rather than ricochets!

 

[Snyper]

However, the 223, 22-250 and 243 will probably travel twice as far before hitting the ground!

That is determined by where you are aiming.

If you're shooting "varmints" smaller than deer, most of your shots should be angled towards the ground.

Using an elevated stand will make things much safer

 

[andym79]

Yere there are a lot of variables, but generally yes if the critter is small most of the time your shots won't be that far above the ground to start with!

I guess really for my scenario to occur you would be talking more of an accidental discharge rather than a miss.

As I don't walk around with a cocked hammer and a round in the chamber , and I never put my finger on the trigger till the prey is in the sight that shouldn't happen.

 

[andym79]

The 218 bee is coming in the next year or two!

 

[Bart B.]

Here's one set of data:

http://www.freehearingtest.com/hia_gunfirenoise.shtml

Another:

http://www.elcaudio.com/tablesforweb.pdf

A 6 db (decibel) increase in sound pressure doubles the noise level.

Search for "firearm sound pressure levels" and there's lots more info.

There are free apps for smart phones that do a decent job measuring sound levels. You may need to have the smartphone some distance from the rifle as all apps won't read levels in the 150 db range. Some apps are better for impulse noise firearms make.

 

[lysanderxiii]

One of the reasons I ask is here in Australia, each time you want to add a rifle to your collection, you need to submit a form (permit to acquire) and write a letter explaining how you justify your need for another centre-fire rifle.

I have rifles that are suitable for hunting on large properties, but want to get one that will allow me to hunt critters on much smaller properties. As I have a weakness for levers I have settle on building a new 25-20 using an un-barreled 1892 action.

I will be explaining that it is better suited to use of smaller properties that more common cartridges like the 223, 22-250 and 243 because it is quieter and because if by some chance a shot should be missed that the projectile will travel a lot less distance than typical modern varmint busters!

I can quantify bullet drop quite easily, but I would like to be able in some way to quantify sound level as well. The reason being to my knowledge, most of the people who stamp the forms don't know the difference between a 375 Winchester and a 375 Cheytac (I know that from experience when my big bore permit got held up!).

Overpressure should be equitable to sound level, however, the exact overpressure and particular gun will produce will depend on many things, type of powder, barrel length, muzzle device (if any), weather....

 

[murf]

and especially the distance from the muzzle to your ear (the x-axis of the above chart).

murf