Why might Avg. Velocity change between reloading sessions?

[Senor_Barney]

I'm seeing a change in velocity from my load between reloading sessions. For example I will load twenty rounds one day...go out and shoot them...and get one average velocity. The load another 20 rounds the next time I go shoot and observe a different average velocity.

Below are the results of two recent sessions. I'm extremely puzzled why the measured velocity dropped off so much in Session #2 given the environmentals seem far more conducive to an acceleration rather than a drop-in velocity with the Hotter ambient temp.


Load Data
41.7gr H4350
140gr Berger Hybrids
Lapua SRP Brass (Virgin, no sizing...nothing)
CCI 450

Session 1:
6 Shots
Avg. Velocity: 2884 woops...2784
SD: 4
ES: 12
Environment: 52F, 78%RH, 30.04hg, DA -490

Session 2:
8 Shots
Avg. Velocity: 2746
SD:4
ES: 9
Environment: 75F, 32%RH, 29.47hg, DA 1684

Equipment:
Magnetospeed V3
AIAX 400 w/ rounds
K&M arbor press for seating
Pm Tools mandrel

So as you can see, even though Session #2 was shot in mid-70s, the velocity actually dropped off 40 FPS from the Session #1 in colder low-50s weather. Totally makes no sense and I feel this data is completely inconclusive. I'm also hesitant to even waste more time.or compents with a 3rd trip to the range until I can narrow down why this happens and what I can do to resolve it.

My Guess:
Powder Scale off: Seems unlikely. I use the Fx120i so I have confidence in its absolute consistency between throes of powder. Though I don't recalibrate during each session and possibly it is under weighing what I thought was 41.7 grains. SD and the velocities were very consistent

Node changed: I ladder tested and found a flat note from 41.6 all the way up to 41.9. So at 41.7 it doesnt seem as if I am in the wrong here. Here was the ladder test from Session #1 w/5 Shot strings
41.6 2782
41.7 2785
41.8 2785
41.9 2794
Although, I've tested ladders before with other barrels and gotten different results at times. Where in one test I'd see a flat spot and then id go and confirm and see a slight increase...

Bad Reloading technique:
Perhaps there is something inconsistent about my reloading from session to session and therefore it would better if I just load hundreds of rounds at once. Is this what others do? If there is...I dont know what it could be because the SDs and the groups are super consistent.

 

[Klay23]

Curious about this too. I’ve seen some similar stuff

 

[Ericsl2]

Do you leave your powder out? Moisture content of your powder could stack with temp change and density altitude. Might slightly alter burn rate? Heard some bench rest guys talking about pouring their powder on a baking sheet and leaving it out for a while to dry it consistently. Not sure the specifics this was just the tail end of a conversation

 

[England]

This is likely due to the variance of small sample size--only six or eight shots. It's like if you took a quarter out of your pocket and flipped it for heads/tails six times then later did it eight times. You might well see a preponderance of heads the first trial and tails the second.

The calculated standard deviation doesn't really become meaningful until you have a sample of 25-30 rounds. At that point, you can predict that 95% of the rounds will have a velocity within +2/-2 SD of the mean.

Oddly enough, I was out shooting a 6.5 CM yesterday with exactly the same load, except that I was using the older Hornady 6.5 140gr ELD-M bullet and their newer version with a slightly higher G7 BC (and the new bullet must be seated 0.040" deeper for the same jump). I wanted to see if the new bullet performed similarly.

I fired 21 rounds of the load with the "old" bullet and my Magnetospeed showed a mean velocity of 2809 fps with a SD of 13.6. Previous testing prior to a long range class had yielded a mean velocity of 2815 fps with a similar sample size. This velocity variance is well within what might be expected.

I then fired 14 rounds of the "new" bullet and found a mean velocity of 2817 fps with an SD of 11.7. Although the "new" bullet loads were slightly faster, this again is well within the expected error. The "new" bullet did produce better 7-shot groups but I'll need to do further comparisons before I begin to believe that either.

Both for velocity and accuracy, groups of 3, 5, or even 8 shots doesn't really model what a 300-round can of the same load might produce.

 

[918v]

Or MS battery is dying

 

[Senor_Barney]

Do you leave your powder out? Moisture content of your powder could stack with temp change and density altitude. Might slightly alter burn rate? Heard some bench rest guys talking about pouring their powder on a baking sheet and leaving it out for a while to dry it consistently. Not sure the specifics this was just the tail end of a conversation

Super odd...super puzzling

I pour powder out of the Bottle for each reloading session into the bulk thrower and the trickler. Whatever excess I have at the end I pour back into the original bottle. They are kept in a cabinet in my garage at a constant 63f and 38% humidity (per the meter in the caninet)

Going back through my notes, I'm wondering if this is limited to H4350 as my Varget loads dont seem to do this or at least not to the same degree.

I'd like to be able to input temps into my Kestrel temp table and go shoot. But at this point I just cannot get consistent, reliable data

 

[nn8734]

This is likely due to the variance of small sample size--only six or eight shots. It's like if you took a quarter out of your pocket and flipped it for heads/tails six times then later did it eight times. You might well see a preponderance of heads the first trial and tails the second.

The calculated standard deviation doesn't really become meaningful until you have a sample of 25-30 rounds. At that point, you can predict that 95% of the rounds will have a velocity within +2/-2 SD of the mean.

Oddly enough, I was out shooting a 6.5 CM yesterday with exactly the same load, except that I was using the older Hornady 6.5 140gr ELD-M bullet and their newer version with a slightly higher G7 BC (and the new bullet must be seated 0.040" deeper for the same jump). I wanted to see if the new bullet performed similarly.

I fired 21 rounds of the load with the "old" bullet and my Magnetospeed showed a mean velocity of 2809 fps with a SD of 13.6. Previous testing prior to a long range class had yielded a mean velocity of 2815 fps with a similar sample size. This velocity variance is well within what might be expected.

I then fired 14 rounds of the "new" bullet and found a mean velocity of 2817 fps with an SD of 11.7. Although the "new" bullet loads were slightly faster, this again is well within the expected error. The "new" bullet did produce better 7-shot groups but I'll need to do further comparisons before I begin to believe that either.

Both for velocity and accuracy, groups of 3, 5, or even 8 shots doesn't really model what a 300-round can of the same load might produce.

This.

It would be nice if people would stop making attributions on their respective populations based on miniscule sample sizes, lol.

Same for ladder testing unless you shoot multiple ladders (complete waste of time/ammo) and maybe you get something vaguley meaningful.

Id shoot it at distance to see if my dope is materially different beyond 600m then work backwards from there if so.

Otherwise I wouldn’t give a shit.

 

[Klay23]

This.

It would be nice if people would stop making attributions on their respective populations based on miniscule sample sizes, lol.

Same for ladder testing unless you shoot multiple ladders (complete waste of time/ammo) and maybe you get something vaguley meaningful.

Id shoot it at distance to see if my dope is materially different beyond 600m then work backwards from there if so.

Otherwise I wouldn’t give a shit.

So what about folks that don’t have 600m?

 

[nn8734]

So what about folks that don’t have 600m?

 

[Klay23]

View attachment 7836163

 

[hlee]

 

[918v]

This is likely due to the variance of small sample size--only six or eight shots. It's like if you took a quarter out of your pocket and flipped it for heads/tails six times then later did it eight times. You might well see a preponderance of heads the first trial and tails the second.

The calculated standard deviation doesn't really become meaningful until you have a sample of 25-30 rounds. At that point, you can predict that 95% of the rounds will have a velocity within +2/-2 SD of the mean.

Oddly enough, I was out shooting a 6.5 CM yesterday with exactly the same load, except that I was using the older Hornady 6.5 140gr ELD-M bullet and their newer version with a slightly higher G7 BC (and the new bullet must be seated 0.040" deeper for the same jump). I wanted to see if the new bullet performed similarly.

I fired 21 rounds of the load with the "old" bullet and my Magnetospeed showed a mean velocity of 2809 fps with a SD of 13.6. Previous testing prior to a long range class had yielded a mean velocity of 2815 fps with a similar sample size. This velocity variance is well within what might be expected.

I then fired 14 rounds of the "new" bullet and found a mean velocity of 2817 fps with an SD of 11.7. Although the "new" bullet loads were slightly faster, this again is well within the expected error. The "new" bullet did produce better 7-shot groups but I'll need to do further comparisons before I begin to believe that either.

Both for velocity and accuracy, groups of 3, 5, or even 8 shots doesn't really model what a 300-round can of the same load might produce.

140 FPS difference. 140!!!

 

[918v]

This.

It would be nice if people would stop making attributions on their respective populations based on miniscule sample sizes, lol.

Same for ladder testing unless you shoot multiple ladders (complete waste of time/ammo) and maybe you get something vaguley meaningful.

Id shoot it at distance to see if my dope is materially different beyond 600m then work backwards from there if so.

Otherwise I wouldn’t give a shit.

Wrong

 

[Senor_Barney]

Or MS battery is dying

Wait....that can have an impact???

Coincidentally...the next session (shooting a different rifle) I did get a "batt low" message on the Magnetospeed.

 

[918v]

I’ve seen my MS do weird shit when the battery was low. I think that’s what your seeing as well.

 

[Senor_Barney]

This is likely due to the variance of small sample size--only six or eight shots. It's like if you took a quarter out of your pocket and flipped it for heads/tails six times then later did it eight times. You might well see a preponderance of heads the first trial and tails the second.

The calculated standard deviation doesn't really become meaningful until you have a sample of 25-30 rounds. At that point, you can predict that 95% of the rounds will have a velocity within +2/-2 SD of the mean.

Oddly enough, I was out shooting a 6.5 CM yesterday with exactly the same load, except that I was using the older Hornady 6.5 140gr ELD-M bullet and their newer version with a slightly higher G7 BC (and the new bullet must be seated 0.040" deeper for the same jump). I wanted to see if the new bullet performed similarly.

I fired 21 rounds of the load with the "old" bullet and my Magnetospeed showed a mean velocity of 2809 fps with a SD of 13.6. Previous testing prior to a long range class had yielded a mean velocity of 2815 fps with a similar sample size. This velocity variance is well within what might be expected.

I then fired 14 rounds of the "new" bullet and found a mean velocity of 2817 fps with an SD of 11.7. Although the "new" bullet loads were slightly faster, this again is well within the expected error. The "new" bullet did produce better 7-shot groups but I'll need to do further comparisons before I begin to believe that either.

Both for velocity and accuracy, groups of 3, 5, or even 8 shots doesn't really model what a 300-round can of the same load might produce.

If I experienced your scenario...id also put it down to normal varience. String of 5 could be +/- vs. The next string of 5 which is why I try to shoot more.

However...I struggle to explain away a 20+ fps slowdown in 20F warmer weather and still sustain single digit SD from an 8 shot group and a 10 shot group.

These were only the ones I measured and observed.

 

[Partsunavailable]

I figured there was a reason the magnetospeed told me it's voltage. It must matter.

 

[D1gger]

+1 on the battery. I don't let the battery get below 7 volts anymore because I was getting readings all over the place

 

[2aBaC̶a̶]

which one is closer to the target velocity? 140fps is a big difference.

 

[Barelstroker]

I reckon the battery scenario is the main contender so far.
My Chrono did weird shit once when the battery was dying.
The next cause might be overall case length is too long & the neck impinging into the carbon ring at the end of the throat or the lead itself if they are that long. Had this happen once as well. Needed some loaded rounds quick & failed my due diligence with the cases. Velocities were way higher & groups went to complete shit when I checked zero.

 

[n2ishun]

Powder is made with ether....I know you've all smelled it.
It outgasses and dries out very quick.
Ether is also extremely flammable and the gas helps the powder to burn at a given rate.
It's like changing the octane rating of your powder.

 

[straightshooter1]

I'm seeing a change in velocity from my load between reloading sessions. For example I will load twenty rounds one day...go out and shoot them...and get one average velocity. The load another 20 rounds the next time I go shoot and observe a different average velocity.

Below are the results of two recent sessions. I'm extremely puzzled why the measured velocity dropped off so much in Session #2 given the environmentals seem far more conducive to an acceleration rather than a drop-in velocity with the Hotter ambient temp.


Load Data
41.7gr H4350
140gr Berger Hybrids
Lapua SRP Brass (Virgin, no sizing...nothing)
CCI 450

Session 1:
6 Shots
Avg. Velocity: 2884
SD: 4
ES: 12
Environment: 52F, 78%RH, 30.04hg, DA -490

Session 2:
8 Shots
Avg. Velocity: 2746
SD:4
ES: 9
Environment: 75F, 32%RH, 29.47hg, DA 1684

Equipment:
Magnetospeed V3
AIAX 400 w/ rounds
K&M arbor press for seating
Pm Tools mandrel

So as you can see, even though Session #2 was shot in mid-70s, the velocity actually dropped off 40 FPS from the Session #1 in colder low-50s weather. Totally makes no sense and I feel this data is completely inconclusive. I'm also hesitant to even waste more time.or compents with a 3rd trip to the range until I can narrow down why this happens and what I can do to resolve it.

My Guess:
Powder Scale off: Seems unlikely. I use the Fx120i so I have confidence in its absolute consistency between throes of powder. Though I don't recalibrate during each session and possibly it is under weighing what I thought was 41.7 grains. SD and the velocities were very consistent

Node changed: I ladder tested and found a flat note from 41.6 all the way up to 41.9. So at 41.7 it doesnt seem as if I am in the wrong here. Here was the ladder test from Session #1 w/5 Shot strings
41.6 2782
41.7 2785
41.8 2785
41.9 2794
Although, I've tested ladders before with other barrels and gotten different results at times. Where in one test I'd see a flat spot and then id go and confirm and see a slight increase...

Bad Reloading technique:
Perhaps there is something inconsistent about my reloading from session to session and therefore it would better if I just load hundreds of rounds at once. Is this what others do? If there is...I dont know what it could be because the SDs and the groups are super consistent.

While other suggestions should be looked at, always keep the following in mind:

 

[acudaowner]

god loves watching people loose there minds he has a great sense of humor at your expense . Like people who get too cough up in that whole bullet length rabbit hole if your a perfectionist your doomed to chase that dragon . Ps it is funny to watch people loose there minds at the range ...

 

[KnowNothing256]

Just reading the title, I figured it was powder moisture (bad seal or loose cap on the jug, etc.) causing lower velocity. However, 140 fps is a really substantial drop, so either it was a distinctly loose cap in a humid environment, or the MS battery was dying. I too have seen mine do wild stuff when it was low, and immediately came to its senses with a fresh juice box.

As for those saying "Oh you need a bigger sample size, then it'll all make sense," you'd all be losing your shit if you had a single load that gave you 140 fps MV spread when subjected to a large sample size. Ridiculous, and nobody here would accept that as a viable load for long-range precision. Clearly something here is wrong, and I'd start with the battery, as others have suggested.

 

[Feniks Technologies]

Assuming people didn’t read the 140fps part.

That’s beyond small sample size issues and such.

Dead battery or some sort of other mechanical issue (scale broken, inputting wrong target weight, etc).

 

[Senor_Barney]

Just reading the title, I figured it was powder moisture (bad seal or loose cap on the jug, etc.) causing lower velocity. However, 140 fps is a really substantial drop, so either it was a distinctly loose cap in a humid environment, or the MS battery was dying. I too have seen mine do wild stuff when it was low, and immediately came to its senses with a fresh juice box.

As for those saying "Oh you need a bigger sample size, then it'll all make sense," you'd all be losing your shit if you had a single load that gave you 140 fps MV spread when subjected to a large sample size. Ridiculous, and nobody here would accept that as a viable load for long-range precision. Clearly something here is wrong, and I'd start with the battery, as others have suggested.

Eff...omg......I realized my typo in the original post. Its not 140fps delta...40fps

2784 at 52F vs 2746 at 75F

The inverse relationship of speed to temp puzzle me still.

 

[Klay23]

Have any of you seen where your muzzle velocity slows down in a typical shot string? I’ve seen it multiple times where say a mv was 2750 and then trickles down to 2730 over a string of 5 shots…. Or maybe even a little slower for example

 

[Feniks Technologies]

Eff...omg......I realized my typo in the original post. Its not 140fps delta...40fps

2784 at 52F vs 2746 at 75F

The inverse relationship of speed to temp puzzle me still.

Well, now we are back into the realm of normal dispersion.

Could be anything from normal shot dispersion, moisture content of powder, etc etc. And as with most things, it’s probably a combination of more than one.

 

[Senor_Barney]

Shucks.

Im in CA where its literally the same humidity and temp for months on end. Hasnt rained in like 5 months. What are the best practices for storing powder in open jugs? Should I leave it in the autotrickler when not reloading?

As such, how does anyone reload reliably if some fluke humidity of the "powder" much less the room have a 40 fps impact one random day on velocity?

I'm in no way a pro or even amateur shooter, but I would like to know that I can reload and get a predictable outcome...

Right now the only predictable thing about these recent loads is they will be unpredictable

 

[Kopfjager1]

With all the variables mentioned, scale drift is certainly a factor if the scale has not warmed up. I notice my Fx120 will drift 0.2-0.4 gr within 10 minutes after turning on.

The sample size is a significant contributor to SD, 3-5 is not a good sample at all, and I would argue 50 rounds is the smallest sample size to determine an accurate SD.

Consistency is key with everything. If you are reloading in the attic (upper floors) or an uninsulated garage, where temperature and humidity swings are prevalent, you're going to notice variations. For those with basements, where temperatures are somewhat stable year-round and humidity typically stays around 50%-60%, you'll probably not see any variation outside of lot changes.

 

[918v]

Shucks.

Im in CA where its literally the same humidity and temp for months on end. Hasnt rained in like 5 months. What are the best practices for storing powder in open jugs? Should I leave it in the autotrickler when not reloading?

As such, how does anyone reload reliably if some fluke humidity of the "powder" much less the room have a 40 fps impact one random day on velocity?

I'm in no way a pro or even amateur shooter, but I would like to know that I can reload and get a predictable outcome...

Right now the only predictable thing about these recent loads is they will be unpredictable

Lookit, I shoot Staball and don’t have a 40 FPS swing. It’s your battery.

 

[Klay23]

What about neck tension? Neck tension could certainly cause some mv variation. Could New brass neck tension have something to do with this also????

 

[Feniks Technologies]

As mentioned, start with the battery.

 

[straightshooter1]

Shucks.

Im in CA where its literally the same humidity and temp for months on end. Hasnt rained in like 5 months. What are the best practices for storing powder in open jugs? Should I leave it in the autotrickler when not reloading?

As such, how does anyone reload reliably if some fluke humidity of the "powder" much less the room have a 40 fps impact one random day on velocity?

I'm in no way a pro or even amateur shooter, but I would like to know that I can reload and get a predictable outcome...

Right now the only predictable thing about these recent loads is they will be unpredictable

Did you watch the video I posted?

 

[Klay23]

Are any of you putting humidity packs like in the video above in your open cans? Seems like from from somewhere research j saw somewhere in another thread that the dryer the powder the hotter the powder. Moisture slowed the burning process and hence mv. So what humidity pack would one suggest?

 

[Baron23]

I'm seeing a change in velocity from my load between reloading sessions. For example I will load twenty rounds one day...go out and shoot them...and get one average velocity. The load another 20 rounds the next time I go shoot and observe a different average velocity.

Below are the results of two recent sessions. I'm extremely puzzled why the measured velocity dropped off so much in Session #2 given the environmentals seem far more conducive to an acceleration rather than a drop-in velocity with the Hotter ambient temp.


Load Data
41.7gr H4350
140gr Berger Hybrids
Lapua SRP Brass (Virgin, no sizing...nothing)
CCI 450

Session 1:
6 Shots
Avg. Velocity: 2884 woops...2784
SD: 4
ES: 12
Environment: 52F, 78%RH, 30.04hg, DA -490

Session 2:
8 Shots
Avg. Velocity: 2746
SD:4
ES: 9
Environment: 75F, 32%RH, 29.47hg, DA 1684

Equipment:
Magnetospeed V3
AIAX 400 w/ rounds
K&M arbor press for seating
Pm Tools mandrel

So as you can see, even though Session #2 was shot in mid-70s, the velocity actually dropped off 40 FPS from the Session #1 in colder low-50s weather. Totally makes no sense and I feel this data is completely inconclusive. I'm also hesitant to even waste more time.or compents with a 3rd trip to the range until I can narrow down why this happens and what I can do to resolve it.

My Guess:
Powder Scale off: Seems unlikely. I use the Fx120i so I have confidence in its absolute consistency between throes of powder. Though I don't recalibrate during each session and possibly it is under weighing what I thought was 41.7 grains. SD and the velocities were very consistent

Node changed: I ladder tested and found a flat note from 41.6 all the way up to 41.9. So at 41.7 it doesnt seem as if I am in the wrong here. Here was the ladder test from Session #1 w/5 Shot strings
41.6 2782
41.7 2785
41.8 2785
41.9 2794
Although, I've tested ladders before with other barrels and gotten different results at times. Where in one test I'd see a flat spot and then id go and confirm and see a slight increase...

Bad Reloading technique:
Perhaps there is something inconsistent about my reloading from session to session and therefore it would better if I just load hundreds of rounds at once. Is this what others do? If there is...I dont know what it could be because the SDs and the groups are super consistent.

So, you have 6 shots in one session and 8 in another and are wondering why you are seeing a 38 fps difference?

Its my view that you don't have enough shots fired and chrono'd to yet even know your true average MVS nor ES and SD.

Again, just my view but collect 30 or more shots and then average them for a good figure and you will also see your ES and SD stabilize.

Its just a fact of statistics that many don't like, but that doesn't make it any less true, IMO.

Best of luck.

P.S. - oops, I see that once again I'm late to the party and am:

hahahaha

 

[Baron23]

Oh, and the problem is those Berger 140 gr Hybrids.....they're no good and you need to sell them to me! haha

Cheers

 

[Baron23]

140 FPS difference. 140!!!

38 FPS difference. 38!!!

;-) haha

 

[Senor_Barney]

Did you watch the video I posted?

I did...i dont have the technology to mess with humidity packs nor does this seem like something that is done by the masses.

Lets say humidoty was the culprit here.
Which spurred my comment that, it seems every bottle is going to have its own humidity level and it is a total crap shoot when you open 3 bottles even from the same lot.

As such, the only way, short of cigar packs, to allow all the powder to "dry out" or "moisten up" to the same humidity would be to open them all up...pour out into a bowl...and let it just sit there. This was, whatever impact my constant 38% humity room is going to have on the powder (speed up / slow down, dry/ moisten) it will have on all the powder at the same time and all the powder will be consistent.

Did I lose anyone....?

 

[918v]

38 FPS difference. 38!!!

;-) haha

Sounded good at the time

 

[918v]

I did...i dont have the technology to mess with humidity packs nor does this seem like something that is done by the masses.

Lets say humidoty was the culprit here.
Which spurred my comment that, it seems every bottle is going to have its own humidity level and it is a total crap shoot when you open 3 bottles even from the same lot.

As such, the only way, short of cigar packs, to allow all the powder to "dry out" or "moisten up" to the same humidity would be to open them all up...pour out into a bowl...and let it just sit there. This was, whatever impact my constant 38% humity room is going to have on the powder (speed up / slow down, dry/ moisten) it will have on all the powder at the same time and all the powder will be consistent.

Did I lose anyone....?

Being we are in Commiefornia we enjoy the benefits of mild weather, coupled with the fact that humidity is somewhat stable inside your house I doubt it has anything to do with the 38!!! FPS swing.

I am more inclined to believe the ether evaporation argument but I don’t see how it could affect the velocity that much over such a short period of time.

I often load at the range, early early mornings, when the humidity often is in the 90% range and don’t get these swings and I pour the powder right there.

 

[straightshooter1]

I did...i dont have the technology to mess with humidity packs nor does this seem like something that is done by the masses.

Lets say humidoty was the culprit here.
Which spurred my comment that, it seems every bottle is going to have its own humidity level and it is a total crap shoot when you open 3 bottles even from the same lot.

As such, the only way, short of cigar packs, to allow all the powder to "dry out" or "moisten up" to the same humidity would be to open them all up...pour out into a bowl...and let it just sit there. This was, whatever impact my constant 38% humity room is going to have on the powder (speed up / slow down, dry/ moisten) it will have on all the powder at the same time and all the powder will be consistent.

Did I lose anyone....?

Here in the Phoenix AZ area we have the issue of very low humidity (like in the 15% and sometimes less vicinity, with huge spikes to 90% when a monsoon storm comes through), which will dry things out quite fast. And of course, the powder drying out does increase burn rate resulting in velocity increase. I've tried to be careful and not leave my powder exposed for very long and pouring out only what might be needed for my case charging operation, only leaving the jug lids off just long enough to pour some powder out. Even so, I was sure that the powder was drying out, but just not sure how much over a period of time. A month ago I decided to actually find out and bought Kestrel Drop as well as some 2-way humidity control packs and started to monitor and record humidity data on some of my powders to actually see what's going on in my environment. Over this time so far, it has been interesting to see the humidity inside the jugs drop and then recover with the use of those control packs. I'm taking measurements only following my reloading cycles of opening and closing my jugs of powder. So, it's going to take a while to accumulate enough data to get a reliable picture as to how my environment actually effects my powder, reloading and shooting. At some point, when I feel I've got enough reliable data, I'll share it.

I'm old and retired, have got the time (as long as I stay healthy) along with enough curiosity to do this.

 

[Klay23]

Here in the Phoenix AZ area we have the issue of very low humidity (like in the 15% and sometimes less vicinity, with huge spikes to 90% when a monsoon storm comes through), which will dry things out quite fast. And of course, the powder drying out does increase burn rate resulting in velocity increase. I've tried to be careful and not leave my powder exposed for very long and pouring out only what might be needed for my case charging operation, only leaving the jug lids off just long enough to pour some powder out. Even so, I was sure that the powder was drying out, but just not sure how much over a period of time. A month ago I decided to actually find out and bought Kestrel Drop as well as some 2-way humidity control packs and started to monitor and record humidity data on some of my powders to actually see what's going on in my environment. Over this time so far, it has been interesting to see the humidity inside the jugs drop and then recover with the use of those control packs. I'm taking measurements only following my reloading cycles of opening and closing my jugs of powder. So, it's going to take a while to accumulate enough data to get a reliable picture as to how my environment actually effects my powder, reloading and shooting. At some point, when I feel I've got enough reliable data, I'll share it.

I'm old and retired, have got the time (as long as I stay healthy) along with enough curiosity to do this.

Need that info…. Haha…

 

[Alpine 338]

Between sessions,

Did you clean your bore or chamber? Run anything through the bore?

Was the rifle sitting in the sun on one of those days heating up the barrel?

 

[Seymour Fish]

I'm seeing a change in velocity from my load between reloading sessions. For example I will load twenty rounds one day...go out and shoot them...and get one average velocity. The load another 20 rounds the next time I go shoot and observe a different average velocity.

Below are the results of two recent sessions. I'm extremely puzzled why the measured velocity dropped off so much in Session #2 given the environmentals seem far more conducive to an acceleration rather than a drop-in velocity with the Hotter ambient temp.


Load Data
41.7gr H4350
140gr Berger Hybrids
Lapua SRP Brass (Virgin, no sizing...nothing)
CCI 450

Session 1:
6 Shots
Avg. Velocity: 2884 woops...2784
SD: 4
ES: 12
Environment: 52F, 78%RH, 30.04hg, DA -490

Session 2:
8 Shots
Avg. Velocity: 2746
SD:4
ES: 9
Environment: 75F, 32%RH, 29.47hg, DA 1684

Equipment:
Magnetospeed V3
AIAX 400 w/ rounds
K&M arbor press for seating
Pm Tools mandrel

So as you can see, even though Session #2 was shot in mid-70s, the velocity actually dropped off 40 FPS from the Session #1 in colder low-50s weather. Totally makes no sense and I feel this data is completely inconclusive. I'm also hesitant to even waste more time.or compents with a 3rd trip to the range until I can narrow down why this happens and what I can do to resolve it.

My Guess:
Powder Scale off: Seems unlikely. I use the Fx120i so I have confidence in its absolute consistency between throes of powder. Though I don't recalibrate during each session and possibly it is under weighing what I thought was 41.7 grains. SD and the velocities were very consistent

Node changed: I ladder tested and found a flat note from 41.6 all the way up to 41.9. So at 41.7 it doesnt seem as if I am in the wrong here. Here was the ladder test from Session #1 w/5 Shot strings
41.6 2782
41.7 2785
41.8 2785
41.9 2794
Although, I've tested ladders before with other barrels and gotten different results at times. Where in one test I'd see a flat spot and then id go and confirm and see a slight increase...

Bad Reloading technique:
Perhaps there is something inconsistent about my reloading from session to session and therefore it would better if I just load hundreds of rounds at once. Is this what others do? If there is...I dont know what it could be because the SDs and the groups are super consistent.

Humidity of powder

 

[Baron23]

I’ll say it again, there is no way, IMO, to discern what’s going on with just two chrono sessions of 5 and then 8 shots and a diff between them of 38 fps.

I encourage the OP to continue to collect chronograph data on his load and just keep adding and averaging.

I suspect he will see his total average converge to a fairly constant value

I bet I could go into my chrono data of 50 shots or more and find a sequential set of values for a 5 shot string and an 8 shot string that will show 38 fps difference in their averages.

Cheers

P.S. - FFS, fixed...dang phone

 

[Senor_Barney]

How are others addressing this situation of humidity assuming it really is the case?

Seems more the exception than the rule to put humidity control packs into bottles? Or are others loading hundreds of rounds all at once?

1 lb of h4350 will load roughly 160 rounds. Not the end of the world time wise...but ill definitely need to neglect my family even more for me to bang out a reloading session that long.

 

[Isaiah's Blacksmith]

The difference is immaterial. Two sessions, 14 shots at less than 1.4%.

 

[Feniks Technologies]

How are others addressing this situation of humidity assuming it really is the case?

Seems more the exception than the rule to put humidity control packs into bottles? Or are others loading hundreds of rounds all at once?

1 lb of h4350 will load roughly 160 rounds. Not the end of the world time wise...but ill definitely need to neglect my family even more for me to bang out a reloading session that long.

Meh, I don’t worry with it.

I make sure my software has a good BC or custom curve that works with the chrono velocity. Chrono that batch (whether it’s been sitting or it’s new ammo), input speed in software, then move on.

That’s far easier than monitoring things much more than keep powder in containers at room temp.

 

[secondofangle2]

I got a kestrel D2 last week and started measuring my powder humidity. All were in the 40-50% range except a pound of RL15. I probably had left that out in a hopper
At some point. I mixed it with another pound and it “balanced out” at 42%.

This humidity thing has led me to the tentative conclusion that I will measure and record the humidity of the powder for each reloading session and the date. It I measure one and it’s an outlier, I don’t know what I will do but probably mix it with another pound as above. Putting a “humidity pack” with my powder seems extreme and untested.