Load Issue with 20 deg temp change?
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Mulligan
Silver $$ Contributor
Don,
here in western Colorado, we have very low humidity (less than 10% many days) and impressive daily temperature swings.
20 degrees in a couple of hours is a common occurrence.
70 in the AM and 95-103 in the afternoon is just normal a July day.
Adjusting powder by about 1/10th for 20 degrees helps for many powders.
An Ezell tuner is the best medicine in my opinion.
I will be watching to see what others think
CW
edit
I will add
The valley floor here is near 5000' in elevation........ so maybe the thin air is causing some of the issues we see?
CW
here in western Colorado, we have very low humidity (less than 10% many days) and impressive daily temperature swings.
20 degrees in a couple of hours is a common occurrence.
70 in the AM and 95-103 in the afternoon is just normal a July day.
Adjusting powder by about 1/10th for 20 degrees helps for many powders.
An Ezell tuner is the best medicine in my opinion.
I will be watching to see what others think
CW
edit
I will add
The valley floor here is near 5000' in elevation........ so maybe the thin air is causing some of the issues we see?
CW
Alex Wheeler
Site $$ Sponsor
Id be looking at something else. Double check the touch point see if you need to adjust seating. In Mt. with the stable powders like H4895 and Varget, same powder charge all year within a kernel or two and thats more like 80+ degrees. In my experience, when a tune is moving around you dont have the right tune to begin with. Now some powders are very temp sensitive. Thats a different story.
moondog
Gold $$ Contributor
I've been monitoring velocity swings lately based on temperature for like 6 months now. This is across 3 different powders so far. H-1000, Varget, and H-4895. They ALL have velocity swings from my experience. 4895, and 1000 20 to 30 fps. Interesting because AB Quantum has a function to input that data.
I believe the saying "don't work up a load in the winter that you will use in the summer". And I think the reverse is true.
Years ago I had found a good load for a 6xc barrel in late summer (pretty hot in AL that time of year). At a mid range match in Memphis in late October, with temps in the 30's& 40's, I could not shoot a good score. Before the last match of the weekend, I put 22 rounds in my pocket to warm them up. Last match I shot a very good score. It shot just like it had at home. Load was h4350 with a 105.
Years ago I had found a good load for a 6xc barrel in late summer (pretty hot in AL that time of year). At a mid range match in Memphis in late October, with temps in the 30's& 40's, I could not shoot a good score. Before the last match of the weekend, I put 22 rounds in my pocket to warm them up. Last match I shot a very good score. It shot just like it had at home. Load was h4350 with a 105.
urbanrifleman
Site $$ Sponsor
What was the velocity change?
People blame the powder for changes in air density. Thick air the bullet goes slower, thin air it goes faster. The main reason people have to re tune is density.
Temp response of Varget at constant density is nearly flat across 50 to 60 degrees.
In their 13th Edition, Speer has a chart showing the change in velocity for changes in ambient temperature in 10-degree increments from 0 to 100 degrees for muzzle velocity from 2631 to 4099.
However, they make a point that even the most carefully prepared reloads can vary as high as 80 f/s when shot at the same temperature.
If we have any professionally trained military / law enforcement snipers on this forum, perhaps they can chime it with their thoughts. The few I've met claim that have procedures for making POI adjustments regarding this element.
Personally, what I have observed is that ball powders are the most sensitive to temperature changes. Also changes in air temperature result is air density changes and I have to make POI adjustments from winter to spring to summer.
Since I don't shoot at the precision level demanded by competitive shooters, I do not have to change loads, just make seasonal POI adjustments.
However, they make a point that even the most carefully prepared reloads can vary as high as 80 f/s when shot at the same temperature.
If we have any professionally trained military / law enforcement snipers on this forum, perhaps they can chime it with their thoughts. The few I've met claim that have procedures for making POI adjustments regarding this element.
Personally, what I have observed is that ball powders are the most sensitive to temperature changes. Also changes in air temperature result is air density changes and I have to make POI adjustments from winter to spring to summer.
Since I don't shoot at the precision level demanded by competitive shooters, I do not have to change loads, just make seasonal POI adjustments.
Amen! Everyone wants to blame the gun, the powder, the scope, morning coffee was to weak. Never they didn't have the gun tuned to start with, they tune with no flags, they have poor bench manners, they skimp on case prep, and the list goes on.So now we will play the nursing game with our load and they wonder why they can't compete. Well get a wide stock, a heavier rifle, a bigger scope, a more expensive rest, that will make it up. I have always had the belief a mass majority of guns on the line are not tuned.
Alexander-M
Gold $$ Contributor
Several years ago I had the opportunity to test the same load, fired with the same rifle within a span of several months with temperatures from 80° to 0°.
Just my 2¢
Alex (Müller)
Just my 2¢
Alex (Müller)
it is impossible to tune a benchrest rifle without wind flags and tuner....IMO of course.
Mulligan
Silver $$ Contributor
Wow,Several years ago I had the opportunity to test the same load, fired with the same rifle within a span of several months with temperatures from 80° to 0°.
View attachment 1664451
Just my 2¢
Alex (Müller)
Great data.......... thanks for sharing.
CW
Alex Wheeler
Site $$ Sponsor
Velocity is not directly linked to tune. If you get in a mentality that my rifle has to shoot xxx fps all the time you will chase your tail.
Mulligan
Silver $$ Contributor
In the short range group game, Nearly all the competitors are loading at the range to keep up with all the changes....... I know a few preloading and using tuners to adjust.
"All the changes" in the above sentence include a lot of variables.
The atmospheric pressure, temperature, relative humidity and several combinations of the three previous weather factors that can have an impact on the system.
Wind is a factor in several ways, it's presence and therefore absence can change a tune. Locally, we normally have either up-slope up-valley winds or down-slope, down-valley winds (diurnal winds). Most of the local shooters cringe when the flags hang. I have seen it with long range as well as short range.....
I believe the tune helps in the wind and may change with the wind conditions.
The Huston Warehouse experiment is a great example of this. What worked outside did not work in the warehouse and what worked in the warehouse did NOT work outside.
I need to run, I will finish up here a bit later.
CW
"All the changes" in the above sentence include a lot of variables.
The atmospheric pressure, temperature, relative humidity and several combinations of the three previous weather factors that can have an impact on the system.
Wind is a factor in several ways, it's presence and therefore absence can change a tune. Locally, we normally have either up-slope up-valley winds or down-slope, down-valley winds (diurnal winds). Most of the local shooters cringe when the flags hang. I have seen it with long range as well as short range.....
I believe the tune helps in the wind and may change with the wind conditions.
The Huston Warehouse experiment is a great example of this. What worked outside did not work in the warehouse and what worked in the warehouse did NOT work outside.
I need to run, I will finish up here a bit later.
CW
AlNyhus
Silver $$ Contributor
It's a close second to tuning based on the D.A. (density altitude).
Mulligan
Silver $$ Contributor
This is true in my testing, but, it is pretty tough for most powders to handle a big swing and stay on point in my experience.
I always see the tune change with atmospheric conditions. Some days I have shot several different loads to stay in tune.
FYI, I seldom use a chronograph...... the target speaks louder without the background noise.
CW
Steve Donlon
Gold $$ Contributor
Think it depends on a little bit of everything and the longer the range you shoot, the more the change is noticed especially in the mountains with the sun warming up the varied landscapes with warm air mixing with cold air and air density changing dramatically. It's not so much staying in tune as it is experience.
urbanrifleman
Site $$ Sponsor
It's a close second to tuning based on the D.A. (density altitude).
I did speak to a very famous shooter one time that dominated benchrest for several years. He tuned by density altitude. Well, I don't wish to overspeak, I'm not sure he did the final tune based on DA, but he said traveling all over the country it gave him a very good baseline from which to work.
100 percent with you on flags. Tuners no and I have been using tuners since most shooters did not know what they were. Can you ever lightly refine a good tune with a tuner, occasionally. I have made a tune shoot rounder if not tighter. I like round. Perhaps your tuning skills could get better? My thought of a tuner is to get back to were I started when I feel the gun is going away from me, period.
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