OzFclass

Hello folks - I know some of you guys are pretty up on engineering stuff . . . and we have something you don't strike very often.

Our range is located very close to the city and some residential areas. The city council has asked us to participate in a noise measuring exercise. This is not a partisan exercise i.e. its without agenda but we don't want to "shoot ourselves in the foot" either.

The measurement point is to be 450 metres directly off the end of our 300 yard mound i.e. at right angles to the line of fire.

I know that we have two noise sources, that from the muzzle and that from the sonic boom of the projectile.

My thoughts on low muzzle noise are to use a long barreled 223, one of mine is 30". We could try and use special loads with a low muzzle pressure (I run Quickload, so no problem to make something up) but I don't really think its worth it. We will try a suppressed rifle as well but we don't want to make a big thing of this in case someone gets the bright idea of mandating them.

The big question is the sonic crack. I know very little about this - I'm guessing that its energy related so using smaller projectiles i.e. 223 is good. I'm also thinking that if we shoot at 300 yards for the test the sonic crack will be less than at 600, where the trajectory is much higher and the duration of the noise longer.

Any thoughts gentlemen?

Thanks
Foster

Foster,

Don't do the testing when the wind is blowing from mound towards the measuring point. Pick your day.

Alan

tentman wrote: We will try a suppressed rifle as well but we don't want to make a big thing of this in case someone gets the bright idea of mandating them.

The big question is the sonic crack. I know very little about this - I'm guessing that its energy related so using smaller projectiles i.e. 223 is good.

At least you live in a country where it's considered polite to suppress the report of your firearm - here it's illegal. My experience as a marker is that the crack from the smaller projectiles is considerably less than that of the bigger ones.

Barry

Yeah - I've done my share of marking and its also my impression that the 223 crack is quite a bit less. Why and by how much would be interesting to know.

G’Day Tentman,

The Dean of my Law Faculty was Professor Braybrooke, a very astute New Zealander who shaped much of my thinking today. I remember him tripping from the top flight of stairs in the lecture theatre and in his attire of mortar board and gown, skidding nose first to the bottom of the long flight of stairs. Much to the audience shock, he got up and brushed himself down and said with a big smile, “Now I am down to your level, I will get on with the lecture.” Rapturous applause followed and he was forever a hero.

So to the point, there is always an agenda in Australia when dealing with public officials. If this is not the case in NZ and you can deal with the facts you are blessed.

To me you are basically dealing with the law of nuisance and essentially the escape of a nuisance from your property which interferes with people’s right to the quiet enjoyment of their land. Of course there are exceptions in common law e.g. that the nuisance was in continuous existence 20 years prior to the new neighbours but there are also statutes that override the common law which are policed by environmental protection authorities for instance. There are also rules that get passed by authorities who act beyond their power to do so, but have never been tested and the culprits often reside in local government and vested interest. It’s complex. Only the lawyers win.

The issue becomes where do I measure to put a value on the escape of the noise? This is not legal advice, but I think legal responsibility begins at your boundary. So testing should be there.

Then you may consider noise level of the average of distances shot along your boundary as you shoot on different mounds.

If on the other hand wise heads can have the closest boundary to a neighbour pass the levels deemed acceptable, then this will assist other ranges who may find themselves in a similar predicament and so set a precedent. Do some unofficial testing to know where you stand.

You would certainly minimise the noise value conducting the tests on a windy day with the sensors upwind. If the tests were conducted on a still day you would bias the results the other way. You may have to re-schedule official testing if the day does not suit.

This is not an engineering problem, but a potential legal one that could be nipped in the bud with negotiation and political solution if you are proactive.

Good luck.

Having been involved with extensive noise testing when we built our new range I have a pretty good laymans knowledge of what needs to be considered. The acoustic engineers completely discounted the sonic crack. It is not very loud compared with the muzzle blast and it dissipates very quickly the further you are away from the bullet flight. We have marking galleries at different distances that are in operation at the same time and so we hear the bullets go past us to a longer range. It is not very loud.

Muzzle blast is a different proposition. That is impulse noise which is considered the most intrusive type of noise and is measured in a different way from your standard decibel meter. The worst-case scenario is a gentle breeze blowing from the firing point to the measuring point. If there is little wind the sound waves dissipate by inverse-square law ie. quite quickly and if the wind is strong then the wind noise itself overpowers the muzzle noise.
There was a computer model from Finland (I think) that allowed you to input various environmental conditions and muzzle blast figures to calculate noise at particular angles and distances from the source. I will try to chase it up.

We found that ambient noises often interfered with the impulse noise measurements eg. birds,sheep or cattle.

Hope this helps

Peter