Which way to Get back in tune?

[Murray Brook]

I feel sure that you will get it back (hope). When and if you do let us know and what you did. TKS

 

[NC/Br Shooter]

I feel sure that you will get it back (hope). When and if you do let us know and what you did. TKS

I will Sir!
And I'll try to post up the numbers.
I'm loading as of this very moment!

 

[urbanrifleman]

I believe you, but I really thought it was the other way around. So if the air is more dense, That means I'll need to add charge .
Regardless, I'll test both ways, but I'm trying to learn this so I'll develop confidence.
Thanks for the reply

Warm air is thinner
Wet air is thinner (less air in the air)

Thin air is faster.

 

[JEFFPPC]

I will add this. If you develoes a good tune with your tuner in neutral when your tune starts to go away it's usually easy to get your tune back with only a few shots fired.

 

[urbanrifleman]

I will Sir!
And I'll try to post up the numbers.
I'm loading as of this very moment!

I talked to a world champ benchrest shooter and he tunes with the chronograph. Watch your speed. The node is always going to be pretty much the same speed. In the summer it will speed up, so you will have to drop your charge to get back to the same speed. The reverse for the winter. Humid air will go faster. Hot humid air is very thin and will be very fast.

This is also why it's critical to not shoot temperature sensitive powders. Because when the speed changes you go out of tune. But people think the only thing that changes the tune is the powder temperature sensitivity. That's not true. Atmospheric conditions change the speed of the bullet in the barrel. It's the exact same logic applied to an airplane wing or a helicopter rotor.

 

[Dimner]

I talked to a world champ benchrest shooter and he tunes with the chronograph. Watch your speed. The node is always going to be pretty much the same speed. In the summer it will speed up, so you will have to drop your charge to get back to the same speed. The reverse for the winter. Humid air will go faster. Hot humid air is very thin and will be very fast.

This is also why it's critical to not shoot temperature sensitive powders. Because when the speed changes you go out of tune. But people think the only thing that changes the tune is the powder temperature sensitivity. That's not true. Atmospheric conditions change the speed of the bullet in the barrel. It's the exact same logic applied to an airplane wing or a helicopter rotor.

This is really good info, I have never thought of taking a really good look at humidity. Now I guess the next question is... how much of a humidity swing will impact velocity. Off to the ballistic calculator I go.

 

[expiper]

you velocity is low for a BR --did you tell us what powder you are burning??? Imusta missed it--but I run mine~ around 200 fps faster than what you are running--what does your pressure look like --primer flow/sticky bolt etc...Roger

 

[Dimner]

This is really good info, I have never thought of taking a really good look at humidity. Now I guess the next question is... how much of a humidity swing will impact velocity. Off to the ballistic calculator I go.

Well, I guess, at least in Michigan, humidity really has very little impact on velocity.

Michigan weather data, with similar temperatures and pressures, I looked for two days that had about as large a swing in humidity as Michigan will get. With the obvious exception of outliers.

Then I used a ballistic calculator for two different bullets and only changed the atmospheric data

Bullet	BC	Drag	Date	T*	Pressure	Humidity	MV	V@600	V Change
Speer 6mm 70	0.282​	G1	5/31/2023​	72.3​	29​	49.9​	3100​	1460.97​
Speer 6mm 70	0.282​	G1	7/15/2023​	70.7​	28.8​	83.2​	3100​	1469.14​	8.17 fps
Hndy 6mm 105 BTHP	0.53​	G1	5/31/2023​	72.3​	29​	49.9​	2800​	1892.45​
Hndy 6mm 105 BTHP	0.53​	G1	7/15/2023​	70.7​	28.8​	83.2​	2800​	1897.95​	5.49 fps

Humidity impacting air density is one less thing for me to worry about.

Edit: Updated error in drag function for 105gr BTHP

 

[gunsandgunsmithing]

Well, I guess, at least in Michigan, humidity really has very little impact on velocity.

Michigan weather data, with similar temperatures and pressures, I looked for two days that had about as large a swing in humidity as Michigan will get. With the obvious exception of outliers.

Then I used a ballistic calculator for two different bullets and only changed the atmospheric data

Bullet	BC	Drag	Date	T*	Pressure	Humidity	MV	V@600	V Change
Speer 6mm 70	0.282​	G1	5/31/2023​	72.3​	29​	49.9​	3100​	1460.97​
Speer 6mm 70	0.282​	G1	7/15/2023​	70.7​	28.8​	83.2​	3100​	1469.14​	8.17 fps
Hndy 6mm 105 BTHP	0.53​	G7	5/31/2023​	72.3​	29​	49.9​	2800​	2318.51​
Hndy 6mm 105 BTHP	0.53​	G7	7/15/2023​	70.7​	28.8​	83.2​	2800​	2321.63​	3.12 fps

Humidity impacting air density is one less thing for me to worry about.

I like to use station pressure vs humidity, da or barometer. It's just another way that doesn't get cluttered with other factors that don't matter, ime. The reason powder temp is used most is because it's the biggest factor, but not the only factor. Also, while velocity has its place, tuning is about the pressure curve and in bore time of the bullet. You can have identical velocities at the muzzle but different in bore times.

I think a spreadsheet for temp and air density will get you a really long way to calculating things but not 100%. Not really sure what else it is but those two are by far the biggest and I estimate temp to be about 4:1 more important that air density...fwiw.

Some powders are certainly more temp sensitive than others but every single one goes out of tune with temp. It's just physics and can't be completely cured. Powder turning from a solid to a gas is a chemical reaction and ALL chemical reactions are temp dependent. No exceptions.

 

[Dimner]

I like to use station pressure vs humidity, da or barometer. It's just another way that doesn't get cluttered with other factors that don't matter, ime. The reason powder temp is used most is because it's the biggest factor, but not the only factor. Also, while velocity has its place, tuning is about the pressure curve and in bore time of the bullet. You can have identical velocities at the muzzle but different in bore times.

I think a spreadsheet for temp and air density will get you a really long way to calculating things but not 100%. Not really sure what else it is but those two are by far the biggest and I estimate temp to be about 4:1 more important that air density...fwiw.

Some powders are certainly more temp sensitive than others but every single one goes out of tune with temp. It's just physics and can't be completely cured. Powder turning from a solid to a gas is a chemical reaction and ALL chemical reactions are temp dependent. No exceptions.

Sorry to further derail this thread, but I think it all helps in the realm of tuning.

I'm pretty ignorant when it comes to weather/atmospheric data past Temperature and humidity. Just so I can get a handle on what you are recommending to use, can you define station pressure as apposed to barometer (which is what I'm assuming I used in my chart)?

Here is the example where I got my data:

Waterford, MI Weather History | Weather Underground

I'm guessing that the pressure they are using is barometric?

 

[gunsandgunsmithing]

Sorry to further derail this thread, but I think it all helps in the realm of tuning.

I'm pretty ignorant when it comes to weather/atmospheric data past Temperature and humidity. Just so I can get a handle on what you are recommending to use, can you define station pressure as apposed to barometer (which is what I'm assuming I used in my chart)?

Here is the example where I got my data:

Waterford, MI Weather History | Weather Underground

I'm guessing that the pressure they are using is barometric?

Baro and da are "corrected" numbers accounting for altitude and humidity, where station pressure is, as I understand it, the weight of a cubic ft of air, uncorrected by anything. I'm sure google has a better answer. Lol!

 

[Dimner]

Baro and da are "corrected" numbers accounting for altitude and humidity, where station pressure is, as I understand it, the weight of a cubic ft of air, uncorrected by anything. I'm sure google has a better answer. Lol!

Gotcha, I think I used station pressure in my chart. I appreciate the info!

 

[AlNyhus]

I talked to a world champ benchrest shooter and he tunes with the chronograph. Watch your speed. The node is always going to be pretty much the same speed. In the summer it will speed up, so you will have to drop your charge to get back to the same speed.

Short range or Long range World Champion?

 

[NC/Br Shooter]

I'll try to get a better picture up. I got to get ready for work here in just a while. I shot a lil while ago at about 2pm. The opposite happened from what I was hoping. My best group was at the highest charge I had loaded. I loaded 29 to 30.2 in .2 grain increments. The only charge not shown is 30 even. If we can't see this target I'll upload another soon. The numbers are the average speed, and then group size
Thanks for all the replies. I have the conditions wrote down. I plan on doing this same test next week. I'm on 134 shots bow

 

[CharlieNC]

I don't shoot BR or know anything about load tuning at a match, but find this topic very interesting and would like to understand more:

Why would atmospheric conditions effect on velocity matter other than the associated powder temperature effect on velocity and therefore bullet exit time? That is external ballistics don't matter much?

Is using a tuner as effective as making small charge weight or seating tweaks?

 

[Bill Norris]

I talked to a world champ benchrest shooter and he tunes with the chronograph. Watch your speed. The node is always going to be pretty much the same speed. In the summer it will speed up, so you will have to drop your charge to get back to the same speed. The reverse for the winter. Humid air will go faster. Hot humid air is very thin and will be very fast.

This is also why it's critical to not shoot temperature sensitive powders. Because when the speed changes you go out of tune. But people think the only thing that changes the tune is the powder temperature sensitivity. That's not true. Atmospheric conditions change the speed of the bullet in the barrel. It's the exact same logic applied to an airplane wing or a helicopter rotor.

I find other atmospheric conditions to affect the tune with either of my rifles more than ambient temps. alone. Barrel temps. with extremely long strings of fire in hot weather have been found by some to affect tune as well. Ambient temps. and/or powder temp. sensitivity alone does not seem to be near as important in my testing.

 

[tom]

This is really good info, I have never thought of taking a really good look at humidity. Now I guess the next question is... how much of a humidity swing will impact velocity. Off to the ballistic calculator I go.

Depends on whether you're asking about humidity as in external (conditions), or as in moisture content in the powder. If your powder is changing, you will have to move the powder for tune some. But not even close to the crony difference. So in that situation, the crony will be dead ass wrong, although I've found the direction to be true, however the amount was something like a 1 to 4 ratio when I tested that.

Tom


Edit to add pictures that took a bit to find






So with my lot of 4895, a 17% change in powder humidity didn't kill it, but it did move it. I get roughly 10ish fps per tenth, so the crony says move it 4 tenths. The paper at 1,051 yards said to move it 1 tenth....So in this case it just tunes at a different speed.



It wasn't the most pleasant day, but I gathered some knowledge lol.

Tom

 

[AlNyhus]

Depends on whether you're asking about humidity as in external (conditions), or as in moisture content in the powder. If your powder is changing, you will have to move the powder for tune some. But not even close to the crony difference. So in that situation, the chrony will be dead ass wrong although I've found the direction to be true, however the amount was something like a 1 to 4 ratio when I tested that.

Tom

This right here. ️ ^^^^^

 

[tom]

I edited in some photos, as it took some digging to find. Of course my goal was to find some manipulation that would shoot better. But after many follow ups, it became apparent that it was tunable and equal no matter what dumb shit I did. At least with that powder lot.

Tom

 

[JFrank]

Probably why my high loads always blow out. :-(