I’m getting confused. I have a brand new high end, custom bench rifle. I am in the process of barrel break in combined with ladder testing for velocity nodes. I loaded up two groups of 15 rounds of ammo. They vary by 0.02 gr. of Varget. I shot the first fifteen and recorded the velocities. Two days ago, the weather broke enough to get back to the range. I started to shoot the second group of fifteen reloads. The velocities for the second group were appreciably slower than the identical reloads in the first group. The only difference was the weather conditions. The second group was shot in much colder and rainy conditions. Is this the reason for disparity in the velocities? The velocities varied roughly around 32 FPS. Do I need to start over and make sure that I test in much more similar weather conditions?
Weather conditions and ladder testing
- Thread starter Topwater
- Start date
Velocity is typically not stable for the 150 rounds or so. This depends on the Caliber. My preference is to work on seating depth in the beginning and then worry about velocity.
I don't do as much load development as I once did since I have established loads that I've used for years but that could change soon due to component unavailability. So, I may be heading back to the bench soon. 
However, getting to your question.
When I do load development, I select days where there is little wind and mirage, and temperatures are not extreme. Typically, I like to do my load development in the mornings in mild weather about 60 to 70 degrees. Cloudy windless days are ideal for me.
As far as temperature, I've noticed some changes in elevation point of impact in as little as 15-to-20-degree temperature changes. I think this is more due to air density changes being denser in colder weather than due to any effect on powder burning when using stick powders. In my experience ball powders are much more sensitive to changes in temperature.
Any variable you can eliminate in load development is going to help analyzing the load potential. So, I would try to conduct load development under similar conditions.
However, getting to your question.When I do load development, I select days where there is little wind and mirage, and temperatures are not extreme. Typically, I like to do my load development in the mornings in mild weather about 60 to 70 degrees. Cloudy windless days are ideal for me.
As far as temperature, I've noticed some changes in elevation point of impact in as little as 15-to-20-degree temperature changes. I think this is more due to air density changes being denser in colder weather than due to any effect on powder burning when using stick powders. In my experience ball powders are much more sensitive to changes in temperature.
Any variable you can eliminate in load development is going to help analyzing the load potential. So, I would try to conduct load development under similar conditions.
life happens varget is temp sensitive.
did you plot the location of the first 15 shots and look for a location node and plot the velocities.
the velocities are useful if you ever shoot in the cold again.
did you plot the location of the first 15 shots and look for a location node and plot the velocities.
the velocities are useful if you ever shoot in the cold again.
Magnetospeed V3
approximately 30 degrees
just over 50 degrees
thats what my FX 120-I says they are
the average difference in muzzle velocity between the two 15 shot strings is a minus 30.166 FPS.
ShtrRdy
Silver $$ Contributor
Couple more questions.
Was the brass that was used for the two separate outings processed at the same time? Were all 30 cartridges loaded before the first outing?
Could the powder have been exposed to a humid environment between the first outing and second outing? (if 15 cartridges were loaded for the first outing and then some time later 15 cartridges were loaded for the second outing)
Was the brass that was used for the two separate outings processed at the same time? Were all 30 cartridges loaded before the first outing?
Could the powder have been exposed to a humid environment between the first outing and second outing? (if 15 cartridges were loaded for the first outing and then some time later 15 cartridges were loaded for the second outing)
Ned Ludd
Silver $$ Contributor
One tenth grain powder is typically good for anywhere from about 5-10 fps velocity differential across a range of different cartridges, i.e. case volumes. Using a charge weight differential of 0.02 gr Varget is unlikely to create a difference in velocity that can even be measured reliably by most chronographs; i.e. less than 2-3 fps or so. I'm going to assume the 0.02 gr charge weight differential you described was due to day-to-day variance, as opposed to a selected charge weight increment.
Nonetheless, the good news is that something caused the 32 fps velocity change. In other words, it almost certainly was not the difference in charge weight of 0.02 gr Varget. Possible sources for the velocity difference might include different atmospheric conditions such as temperature, humidity, etc. Alternatively, variance in case volume, neck tension, primer brisance, powder moisture content, barrel lapping-in status etc., etc., etc., could also contribute to velocity variance. Unfortunately, sometimes the only way to know for sure is to test every possible variable independently until the culprit(s) are found.
Rather than testing a bazillion different potential sources for the velocity differential, I would suggest making sure the barrel is fully lapped-in and producing consistent velocity from a given charge weight before doing any further serious load development. In the event that the 0.02 gr differential you described was an intended charge weight increment, I would also suggest using a more realistic charge weight increment; i.e. not less than 0.1 gr. You can always go back and fine-tune charge weight later if you think it's necessary. Further, I would suggest not doing serious load development on days where the temperature varies markedly. If you can't get a sufficient number of days to test with reasonably stable temps, I'd wait until you can, or try to do more testing on a single day. If your velocity is varying by as much as 32 fps for a given charge weight on different days, load development will be challenging at best.
Nonetheless, the good news is that something caused the 32 fps velocity change. In other words, it almost certainly was not the difference in charge weight of 0.02 gr Varget. Possible sources for the velocity difference might include different atmospheric conditions such as temperature, humidity, etc. Alternatively, variance in case volume, neck tension, primer brisance, powder moisture content, barrel lapping-in status etc., etc., etc., could also contribute to velocity variance. Unfortunately, sometimes the only way to know for sure is to test every possible variable independently until the culprit(s) are found.
Rather than testing a bazillion different potential sources for the velocity differential, I would suggest making sure the barrel is fully lapped-in and producing consistent velocity from a given charge weight before doing any further serious load development. In the event that the 0.02 gr differential you described was an intended charge weight increment, I would also suggest using a more realistic charge weight increment; i.e. not less than 0.1 gr. You can always go back and fine-tune charge weight later if you think it's necessary. Further, I would suggest not doing serious load development on days where the temperature varies markedly. If you can't get a sufficient number of days to test with reasonably stable temps, I'd wait until you can, or try to do more testing on a single day. If your velocity is varying by as much as 32 fps for a given charge weight on different days, load development will be challenging at best.
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I didn’t mention it but I have only 66 rounds down the barrel. It was suggested by some knowledgeable friends that velocities will not settle down until it has 100 rounds or so. I keep thinking that the drastic difference in rainy humidity between the two shooting sessions mat be the culprit. ………all 30 rounds were loaded at the same time. ……….and yes, the 0.02 gr. variances in powder weight was intentional.
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