If temperature causes variations in speed is it worth adjusting charge weight

[the boy]

I was shooting over the last few daysto check zero for a match and the temperature was up from 70 deg F to 91 deg F. the temperatures will get a good deal warmer yet like well over 100. I noticed that the average speed of the load went up by 14fps and the SD went from 4.1 to 10.3 fps. Groups were still great a little over .4 for both days. sample size was 20 shot groups.
Rifle is a .260 rem bolt gun using lapua brass, Berger 140 elite hunter, CCI BR2 primers and H 4350 which is really ADI 2209 an Australian made powder exported to the USA and rebranded. Chrono was Dopler radar, temp measurement was with Kestrel drop.
Question is are shooters adjusting their loads to keep the speed at a set point? At distance 900 plus yards good SD's matter and I was disappointed to see the shift. on previous testing I have found .1 of a grain equals roughly 15 fps so maybe bringing the charge back in warm conditions is a plan???

 

[Beiruty]

I was shooting over the last few daysto check zero for a match and the temperature was up from 70 deg F to 91 deg F. the temperatures will get a good deal warmer yet like well over 100. I noticed that the average speed of the load went up by 14fps and the SD went from 4.1 to 10.3 fps. Groups were still great a little over .4 for both days. sample size was 20 shot groups.
Rifle is a .260 rem bolt gun using lapua brass, Berger 140 elite hunter, CCI BR2 primers and H 4350 which is really ADI 2209 an Australian made powder exported to the USA and rebranded. Chrono was Dopler radar, temp measurement was with Kestrel drop.
Question is are shooters adjusting their loads to keep the speed at a set point? At distance 900 plus yards good SD's matter and I was disappointed to see the shift. on previous testing I have found .1 of a grain equals roughly 15 fps so maybe bringing the charge back in warm conditions is a plan???

Would you be able to correct (dial up or dial down) for 15fps difference at the distance you are shooting? I guess not. Check and Verify

 

[Ned Ludd]

The real question is whether the change in velocity puts the load out of tune. If not, there is no reason to adjust the charge weight. If yes, then you absolutely want to adjust the charge weight as best you can for the temperature range you will encounter in the match.

I've observed this going both ways, meaning I've had loads that seemed to shoot well even with a 30-40 degree decrease in temp that caused perhaps a 15-20 fps decrease in velocity, and loads where if the velocity dropped by more than about 10-15 fps, they no longer shot nearly as well. The only way to know with certainty is to test across a reasonable range of temperatures.

In my hands, the likelihood that a load will shoot well even with a change in velocity due to temperature differences is also greatly increased by the direction of the temperature change. A load developed at a higher temperature has much better odds of still shooting well when the temp (and velocity) drop. I don't think I've ever had a load that was developed in colder temps that still worked well when the temp went up far enough to increase velocity markedly. You may also have to be concerned about going way over-pressure in the second scenario if you load is already close to MAX at the lower temperature.

 

[RegionRat]

Depending on the validity of the first SD, the second one might still be normal.

To see if the speed change for a temp change from 70 to 91 makes sense, I would check a simulation.

H4350 is well known for being fairly insensitive, but nothing is perfect.

The type of shooting being discussed is as important as telling the caliber. Sounds like you are pre-loading, so if you think the tune is better with 0.1 less for the hot days, then the only way to know is to go test.

Sometimes, group sizes out past 600 yards correlate to velocity stats, sometimes they don't.

Just keep in mind how noisy the SD/ES stats can be, and still be within normal.

 

[ebb]

Bench rest shooters tune the 6PPCs by temp. one guy did a study and decided 6 degrees could be compensated for with .1 of a grain of powder IIRC.

 

[mikecr]

Well, there may be 3 things changing; barrel, bolt, powder.
You can make sure the striking system is not dominated by a lube affected by temp variance.
You can keep a barrel covered until shooting, and then at an adjusted rate.
You can hold ammo at the same temp that you developed at.
Just ideas to consider

 

[Bill K]

If you are still getting the accuracy you did or want, then it probably would not make much, if any difference.

 

[the boy]

Depending on the validity of the first SD, the second one might still be normal.

To see if the speed change for a temp change from 70 to 91 makes sense, I would check a simulation.

H4350 is well known for being fairly insensitive, but nothing is perfect.

The type of shooting being discussed is as important as telling the caliber. Sounds like you are pre-loading, so if you think the tune is better with 0.1 less for the hot days, then the only way to know is to go test.

Sometimes, group sizes out past 600 yards correlate to velocity stats, sometimes they don't.

Just keep in mind how noisy the SD/ES stats can be, and still be within normal.

total right about doing more testing. I'm shooting large sample sizes around 20 shots to try and eliminate false conclusions. I was wondering if match shooters adjust their loads dependent on the tempreatures?

 

[RegionRat]

total right about doing more testing. I'm shooting large sample sizes around 20 shots to try and eliminate false conclusions. I was wondering if match shooters adjust their loads dependent on the tempreatures?

Lots of different things are called "match shooting" so context is important here.

If you ever watch Short Range BR shooters who can load between target relays, you can learn how they compensate for conditions. Keep in mind most of the record groups are 5 shots with unlimited sighters, within a time limit. This makes loading to conditions possible. Certainly worth a visit to a match to watch and learn.

However, if the ammo cannot be loaded on the spot between target relays, then the situation calls for load tuning ahead of time. Getting the tune into the widest forgiving node will sometimes take precedent over a tight picky node that falls out with temperature or barrel condition. Using the best powders for temperature insensitivity is also very important if you expect temp swings.

 

[JFrank]

total right about doing more testing. I'm shooting large sample sizes around 20 shots to try and eliminate false conclusions. I was wondering if match shooters adjust their loads dependent on the tempreatures?

Constantly

 

[Doom]

Years ago shooters that shot 1000yds with 308 would have two or more different rounds for various temperature when they were pushing the limits of the cartridge at that range. A cold weather load could lock up a rifle at summer conditions and would take it out of the "node". Most newer powders (and formulations of some older ones) are not as temperature sensitive. If your precision doesn't suffer it makes little sense to worry about the deviation in velocity.

 

[Ray123]

I never adjusted the powder in relation to the outside temperature. It seems to me you're just adding another variable to varying conditions you can not control. The same exact weight of a certain powder burns differently and puts out slightly different results in the same case at the same outside conditions....because its made of blended ingredients and coatings not identical in each grain of powder... not to mention primer inconsistency and bullets not exactally the same
either...So...don't worry about the small stuff you cannot control. Your brain is the main instrument of control, use it ....and train the mind to shoot.
Try this, ... this winter learn to shoot 1000 yd targets with no benches, no electronic gadgets, with snow on the ground & snowing, or in cold rain, with freezing fingers in the prone...or even at 100 yds in a snow storm, and high wind. Try to Shoot your personal best here, the more uncomfortable the better. Trust your mind as you learn...that extra kernel of powder in the case will never enter into the equation, as you try to feel the trigger with frozen numb fingers, and your breath fogs the scope, or your glasses adding to the frustration and prolonged discomfort of laying in a now puddle of freezing water as freezing rain falls on the 6" of snow covered ground. "The only easy day, was yesterday." This is my hobby and it's supposed to be fun, and I'm too old for this crap,..but some time must be spent the harsh reality of truth and mind over matter situations, to find your true mental ability to train your mind....and that's where it's really at...the caliber or cartridge you use is almost unimportant.

 

[JEFFPPC]

I have found developing loads in 60 to 70 degrees they usually hold together even in the upper 80s. But shooting in zero degree usually requires at least an additional .2 or even .3 to hold together. I am referring to bench rest with cartridges holding up to mid 30s grains of powder . I am usually in an upper node

 

[mikecr]

I would like whatever you're smoking Ray123.
But the truth is -everything is under our control. It's all in our choices.

 

[BigBolt]

Your bullet’s trajectory flattens as the temperature increases and the air density reduces, and muzzle velocity also increases with temperature.

Bullet drop at 300 meters is almost non-existent — a few centimeters at most. This explains why experienced hunters may not notice the effects of temperatures on a bullet path since they don’t need to account for it to hit targets. At long distances, gauging the temperature is crucial for accuracy.

Temperature does affect bullet trajectory, let’s look at how you can correct the situation to ensure spot-on accuracy in hot or cold weather.

Indeed, many sharpshooters and military snipers are taught how to use 1 Minute of Angle (MOA) shift for every 20 degrees change in ambient temperature. However, it would be best to determine how temperature change affects your rifle and cartridge on your own.

The process is pretty straightforward:

To nail how temperature variation affects your muzzle’s velocity, you must determine your propellant’s sensitivity to temperature changes.

You can do this by shooting your rifle through a chronograph and recording the muzzle’s velocity over different temperatures. That way, you can figure out how a 10- or 25-degree Celsius change will affect the velocity.

If you’re using ballistics software to generate trajectory or clicks needed to hit various targets, work with your rifle’s velocity as it would be under the current temperature.

All you need for this one is a ballistic calculator. Enter the current atmospherics — relative humidity, barometric pressure, and temperature — your calculator will take it from there.

Humidity can affect your shooting, but how much of an impact are we talking about? Does even humidity matter since the impact is negligible?

At close ranges, humidity doesn’t matter. However, the impact is significantly noticeable when shooting targets over longer distances

You can calculate how humidity affects your shooting using a ballistic calculator. Top ballistic apps for Android and iOS include:

• iSnipe
• Strelok Pro
• Ballistic Advanced Edition

Alternatively, you can use a Garmin smartwatch to calculate humidity variations.

Pro Tip: You can use a relative humidity of 50% if you cannot determine the humidity using the solutions above.

While temperature and humidity affect your shooting, you can determine the two elements using ballistic solutions. Better yet, platforms like Revic App allow you to measure the effects of temperature and humidity if you’re connected to a local weather station.

 

[mikecr]

Bullet drop at 300 meters is almost non-existent — a few centimeters at most.

You might wanna try one of them apps yourself...

 

[Doom]

the SD went from 4.1 to 10.3 fps.

If these were 20 round samples then an F-Test would say that here is a 95% probably that the 4.1 is in fact lower than the 10.3. But there is a caveat here. The chronograph is probably +/- 2.7 fps so that increases the uncertainty in the velocity measurements. Normally the accuracy should be 4x smaller than the rest of the errors/uncertainty to have negligible effect on the uncertainty. When you get into the single digits it has an effect Just understand that the 10.3 is probably a more accurate measure of the test SD than 4.1.