Does humidity affect rifle tune?

[1KBR]

I was looking at the kestrel wind meters and noticed one of them can read humidity. Is there any practical real world change in barrel tune with different humidity?

 

[Alex Wheeler]

I lived in a very humid state, and moved to a very dry state. The tune of my rifle did not change. Sorry, its not scientific. Humidity does effect external ballistics though.

 

[Immike]

The only thing that I am aware of is that the powder can gain weight from exposure to humid air. I haven't been able to detect any changes in the tune from it.

 

[GSPV]

At a given setting, the weight of powder thrown by a volumetric dispenser changes as humidity changes.

The velocity of a given powder charge varies by temperature. The higher the temperature, the less energy loss to the barrel and the more that goes into making velocity.

Velocity is a stand in for exit time. It works pretty well. I wish that I had a way to plot exit time directly.

The bottom line is that if you eliminate the thrown charges, you eliminate humidity as a variable. You can do this in a number of ways. Since I shoot short range, I can use a ChargeMaster on a battery pack at the range.

You can then keep a rifle in tune by keeping velocity constant throughout the day. Pretty easy to plot with Excel using the linear regression function.

You can do the same thing by plotting tuner change required to stay in tune as a function of temperature.

But, hey, I'm just a duffer.

 

[Immike]

At a given setting, the weight of powder thrown by a volumetric dispenser changes as humidity changes.

The velocity of a given powder charge varies by temperature. The higher the temperature, the less energy loss to the barrel and the more that goes into making velocity.

Velocity is a stand in for exit time. It works pretty well. I wish that I had a way to plot exit time directly.

The bottom line is that if you eliminate the thrown charges, you eliminate humidity as a variable. You can do this in a number of ways. Since I shoot short range, I can use a ChargeMaster on a battery pack at the range.

You can then keep a rifle in tune by keeping velocity constant throughout the day. Pretty easy to plot with Excel using the linear regression function.

You can do the same thing by plotting tuner change required to stay in tune as a function of temperature.

But, hey, I'm just a duffer.

Just for conversation purposes, wouldn't the weight be more a issue with the scale rather than the thrower?

 

[amlevin]

I lived in a very humid state, and moved to a very dry state.

I had to work in a very "dry" state once. I just brought my own and there was no problem. 8) 8)

As for humidity affecting the "tune", if you're shooting LR and are concerned with Density Altitude then humidity can be a factor. Temperature and Altitude are primary factors but increased humidity will also increase D/A to a lesser degree.

If you're shooting at the extreme ranges you'll probably pay more attention to Density Altitude including humidity, Latitude, compass heading of the shot, and coriolis effect, than one who's shooting 100-300 yards.

 

[LHSmith]

No explanation offered , but N-133 in a 6 PPC starts acting "goofy" below 30% RH. So humidity certainly does affect tune (with certain powders at least) as can be attested by numerous HOF BR members.
Theorize on the "why" if you must, but I just accept it and move on.

 

[GSPV]

Just for conversation purposes, wouldn't the weight be more a issue with the scale rather than the thrower?

Change in humidity doesn't appreciably change the weight of the powder charge. Note "appreciably".

As the day goes in, particularly out west, the humidity drops like a rock. It causes the powder, especially N-133, to "fluff up" (quote from HoF member right there) and the weight of the charge thrown by volume to likewise drop like a rock.

The same thing can happen in an air conditioned loading room/trailer.

I don't like volumetric drops for that reason.

"We shoot by weight, but we throw by volume". - Jack Neary. If you google his name, you should get to a YouTube of one of his n-133 tuning sessions.

 

[stool]

yes

 

[BoydAllen]

Some time back, an article was published in Precision Shooting magazine that spoke to this very issue. Without reproducing the whole thing, let me mention some salient results that were reported in that article. The extreme spread in weight of the same exact particles of powder (133 I believe), comparing completely dessicated with completely humidified was 2%. When samples were fired using both conditions for comparison, the difference in velocity was 320 FPS. Cases were weighed, and then charges were placed in them using powder from a freshly opened new container. These cases were placed in a round wooden block that would fit through the mouth of a glass jar. The block had long screws on its bottom side that extended to form legs to keep the blocks and cases out of direct contact with what was in the bottom of the jar. A desiccant (probably silica gel, I forget) was placed in the bottom of the jar below the block with the cases of powder in it, and the jar was sealed and left that way for long enough for the moisture to be drawn out of the powder. Later the same thing was done placing water in the bottom of the jar.
My point is that the difference in velocity far exceeded any difference in weight caused by moisture content, or lack of it. This test was somewhat unique in that it produced hard data, something that is usually sorely lacking in discussions of this sort. For those of you who read the article, and may have a copy in front of you, please feel free to correct what I have written from memory.

 

[Immike]

I remember reading this article. The test was so extreme that it would be hard to duplicate out of the test tube. I won't leave powder in my scale after reading that and return it to the jug immediately after weighing charges.

 

[BoydAllen]

The other kicker is that almost no one except short range group shooters would run into some of this stuff...but they do. On a day when the temperature starts out in the 70s and goes up to the low hundreds, and the humidity makes a big swing in the process, to under 30%, it really comes into play, particularly with 133. When I read of conclusions drawn where the conditions are generally such that the warm weather humidity is always quite a bit over 30% I think to myself that while those conclusions prescriptions may be spot on there, they may not be elsewhere. Here is a test that anyone can easily try. On a day that is going to have a hot dry afternoon, open a new container of powder. Charge a dozen sized cases, and for half of them seat the bullets. For the other half, cork them some way, so that they may be transported without spilling. When you get to the range uncork the cases that do not have bullets, and set these aside, in the open air, beside the cases that had had bullets seated. Just before you go home, seat bullets in the open cases (to the same depth) and chronograph both sets.

 

[GerryM]

Yes it does The powder draws moisture from the air while loading.

 

[LHSmith]

^^^Yep, while most smokeless powders are non-hydroscopic, they can attract moisture through ADsorption.

 

[Grimstod]

Watch this video. Humidity is a very misunderstood subject. Especially in Hollywood.

http://www.youtube.com/watch?v=nthZ7RHD3yA&feature=share&list=PLJUaiRIEduNXoal2_PkBZi0vDCIcEPxUn&index=28

 

[1KBR]

I should have clarified. All of my reloading will be done in my usual basement at home where the humidity doesn't change much. When I was referring to humidity, I meant will the humidity at the range affect tune in ammo which is already loaded. I realise that humidity may affect me if I load at the range as 6 PPC users do with their N133, but I load my H4350 and H4831sc at home.

 

[Immike]

I should have clarified. All of my reloading will be done in my usual basement at home where the humidity doesn't change much. When I was referring to humidity, I meant will the humidity at the range affect tune in ammo which is already loaded. I realise that humidity may affect me if I load at the range as 6 PPC users do with their N133, but I load my H4350 and H4831sc at home.
[/quote

I was getting ready to pull up your original post and point this out... I haven't had a tune problem going from my humid area to the dry parts of the country with loaded ammo.

 

[LHSmith]

IMHO, yes conditions (temp., RH, Barometric pressure) affect the rifles tune which is why the vast majority of Benchrest Competitors continually adjust the load to keep in tune. They all do not shoot N133. Even with a tuner the powder has to be operating at it's highest efficiency. A competitive tune is more than just barrel harmonics.

 

[GSPV]

Sounds like you have a long-range rig.

I'll opt out of it. At short range, temperature is the largest factor. There are lots of ideas, but the science is behind temperature.

 

[ebb]

if you want to know go to JBM or other ballistic calculator and run a drop chart and change only the humidity number and run another chart. It will surprise you. There is a reason the computer wants to know the humidity when it does calcs.