Temperature Insensitivity of Varget, IMR 4166, IMR 4064, N140 for .308 F-TR

Discussion in 'Reloading Forum (All Calibers)' started by BillC79, Mar 25, 2020.

  1. BillC79

    BillC79 Silver $$ Contributor

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    I recently tested temperature sensitivity of several powders against that of Varget for my .308 F-TR rifle with 200.20X bullets. The goal was to identify powders that showed similar, or better, insensitivity to temperature-induced velocity changes within the temperature range that I regularly shoot in North Central Florida (34-99° F). I have attached a summary graph of the results as an image. The full study with data and analysis is on my website at: https://wlcastleman.com/equip/shoot/varget/index.htm

    tempvsfps_label_900.jpg

    For experienced shooters, much of what I describe probably falls into “rediscovery of the wheel” territory. However, others may find the information useful. So I am posting the study and results for comment and criticism.

    The major findings of value to me from this study were:
    1) Over the full temperature range (34-99° F): Varget and Vihtavuori N140 showed comparable temperature insensitivity
    2) In the high temperature range from 77-99° F, IMR 4166 was much more insensitive to temperature-induced velocity increases than was Varget.
    3) In the low temperature range from 34-77° F, IMR-4064 provided the greatest temperature insensitivity and outperformed Varget.

    I will continue to revise the website over the next several weeks. Thank you in advance to those who look at the study on the website and provide comment and suggestions for improvement.
     
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  2. perazziguy

    perazziguy

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    Thank you for your testing. I have and use varget as well as 4064. Both are great powders. I have not used N140 or 4166. They are on the to try list.
    Jonathan Taylor
     
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  3. RegionRat

    RegionRat

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    Nice start to the testing Bill. I also agree with the notes you made in the link about self-critique and lessons learned.

    While bbl heating during strings can be an issue, with only 3 shots per point, it is hard to draw conclusions. The velocities of each shot could be presented in lieu of the SD which isn't meaningful for an N=3. The additional data points would help shed light similar to the concept of finer temperature steps. We would know if there was just dispersion and noise, or a real trend line similar to the QL predictions.

    In any case, great effort at collection and reporting, then sharing openly is to be commended. Thanks for your efforts.

    ETA: Have you considered H4350 as another standard with a good temp sensitivity baseline?
     
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  4. Bc'z

    Bc'z Gold $$ Contributor

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    Thanks for the info.
    @BillC79 did you change load charge weights?
    I'm mostly concerned with 4166 to varget.
    Brett
     
  5. BillC79

    BillC79 Silver $$ Contributor

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    Thank you for your comments, RegionRat
    I agree with you that based upon the limited number of replicates for each mean point and based upon the wide temperature range between points that caution is warranted in interpreting the data. However, this initial pilot study was conducted to identify candidates for further study as Varget replacements. There is reason to be optimistic that IMR 4166 is at least as temperature insensitive as Varget between 77 and 99° F. There is also reason to be optimistic that IMR 4064 has greater temperature insensitivity than Varget between 34 and 77° F. Additional testing is needed to confirm these optimistic preliminary interpretations.
    For now, I plan to concentrate on the warmer end of the spectrum with Varget and IMR-4166. My current match load uses a 208gr ELD-M with Varget to achieve a velocity over 2600 FPS at 74°F. I can’t get enough N140 or H4350 in a case to reach that velocity, and my initial temperature response study with IMR 4064 tells me I’ll hit over pressure levels well before 99°F. A preliminary study plan is to have 5 replicates each with Varget and IMR 4166 at 5 degree separation points between 70 and 100.
     
  6. BillC79

    BillC79 Silver $$ Contributor

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    Yes, if you go to the web page that I put up, you will see that I am using different charge weights for IMR 4166 and Varget to achieve similar velocities. Or am I missing the point of your questions?
     
  7. Bc'z

    Bc'z Gold $$ Contributor

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    No you got it. Thanks
    I checked hogdens website and noticed it doesn't take quite as much IMR4166 as Varget for my applications in my 6.5cm.
    Edit, I'll work loads up accordingly to my standard procedure.
     
  8. Ned Ludd

    Ned Ludd Gold $$ Contributor

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    Bill - nice study, thanks for sharing!

    I have a couple of observations regarding your graph and conclusions. From a purely scientific point of reference, standard graphing format is to use straight lines in between individual data points as the use of curved lines in between data points implies more data points than are actually present/visible. In other words, there is actually no data in between each of your data points, so they should be connected with a straight line, as a curve implies there are actually more measurements to support the existence of the curved line. The practice of using a straight line in between individual data points can sometimes be tormenting as the human eye and brain really wants to put a curve there.

    The velocity change in terms of fps per degree is then calculated from the slope of the straight line segment in between two actual data points. It is simple to calculate by subtracting the velocity at a lower temperature point from the velocity at a higher temperature point and divide by the temperature differential, which is how you appear to have made the calculations from the Excel spreadsheet.

    Another thing to be aware of when conducting tests of this sort is that a significant amount of powder burns within the barrel (i.e. outside of the chamber/case). Therefore, the temperature of the barrel also plays a role in powder burn rate, as does warming/cooling of the case and powder in time between when it was chambered and fired. Ideally, we would like to conduct such a test in which the temperature of the rifle and ammunition were the same as the ambient temperature. Unfortunately, it is rarely ever feasible to do a study that way, so chambering a cartridge equilibrated at some specific temperature in a rifle that is equilibrated at ambient temperature and pulling the trigger quickly is the best we can usually hope to do. Regardless, I don't think these considerations would have any impact on the main conclusions from your test results, they are just things to think about.

    I hope you had fun carrying out this test, in addition to gaining some useful information using your specific setup. I am a big proponent of doing your own testing where possible, even if it seems like it might be replicating something that has already been done. I personally enjoy doing these types of studies quite a bit. Different setups are not always the same and this is how we learn more about how things work in our own hands. Thanks again for posting your results!

    FWIW - Below is a link to another test that includes the two powders that gave the least temperature sensitivity in your test. Although it was done with a 6.5x47 Lapua cartridge, it might be of interest to you for the purpose of comparison:

    https://precisionrifleblog.com/2016/06/19/powder-temp-stability-hodgdon-extreme-vs-imr-enduron/
     
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  9. dmoran

    dmoran Donovan Moran Silver $$ Contributor

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    @Ned Ludd
    Like above, often you depict how others should conduct tests and/or present there data, think it would be great to see yours. From your detailed inputs it would seem you have plenty of experience, so please do share with us some of your own powder sensitivity tests !.!.!
     
    Last edited: Mar 26, 2020
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  10. daleboy

    daleboy Gold $$ Contributor

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    +1 Would love to see it, I am always interested in "real world " experience .

    To the OP, thanks for posting your findings . I am following this thread with interest. I use 3 of the 4 powders, and would like to learn all I can on the subject .
     
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  11. WyleWD

    WyleWD Silver $$ Contributor

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    Are the Extreme Spread(s) for each load depicted in this graph too? Or am I mis-interpreting the abbreviated vertical bars at each load's data point? WD
     
  12. BillC79

    BillC79 Silver $$ Contributor

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    Ned, Thank you for your helpful comments and suggestions. The test conducted by Patrick Middlebrook and reported by Cal Zant that you cite was the inspiration for the test that I ran. Unfortunately, that study makes a number of assumptions based on one data point between 25°F and 140°F that isn’t particularly helpful to those of us who shoot in the vast environmental territory between those points. My first tests only had two data points between 34°F and 99°F, and I had the graphics program connect them with a splined line, rather than a straight line. Similar weak assumptions are made when connecting widely separated data points with either straight or curved lines. The effect of temperature on the rate of chemical reactions is not linear using linear data axes. So, in the absence of more data (or a degree in chemistry or chemical engineering), I am comfortable in taking the splined-line approach as an approximation until I have more data.
     
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  13. BillC79

    BillC79 Silver $$ Contributor

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    The vertical bars are the standard deviation, an indication of the spread (or variability) of the 3 values per point. I address the most likely reasons for the variability in the data on the website.
     
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  14. daleboy

    daleboy Gold $$ Contributor

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    Key point right there..... thanks for following up on this .

    "Unfortunately, that study makes a number of assumptions based on one data point between 25°F and 140°F"
     
  15. JEFFPPC

    JEFFPPC Silver $$ Contributor

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    Forget the big words, all powder is subject to change from temperature. Temperature insensitivity is a marketing term. Only accurate answer is test your loads in the temps you will shoot to determine where you need to add or subtract powder.
     
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  16. Acyr

    Acyr Mediocre FTR Shooter Gold $$ Contributor

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    Thanks for taking the time to test these powders. I have long suspected common powders like varget do not follow a stable path as ambient and barrel temps increase. Rather they tend to rise at an accelerated rate somewhere in the range of temps we normally use them, lets say 50-105 degrees for most of the country. Your breaking it down to smaller blocks of temps helps us understand exactly how we can expect our loads behave in more specific temp conditions (lets say 50-80 or 80-100 for example) and adjust our loads accordingly depending on the weather forecast. This is important to us F Class shooters since we have to load our 75 rounds or so ahead of time.
    I look forward to more of your testing data.
     
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  17. CharlieNC

    CharlieNC Silver $$ Contributor

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    Try n=10 and get back with me. In the meanwhile we can all see whatever we want to suit our preconceived notions.
     
  18. BillC79

    BillC79 Silver $$ Contributor

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    Thanks for the suggestion of n=10. Do you have personal experience or publication data that you can post or cite to support your suggestion that 10 replicates will provide substantially better information than 5 at each temperature and powder point? I would need something more than a preconceived notion to justify the time and expense.
    As the next test design is evolving, it appears that it will be n=5 between Varget and IMR 4166 at roughly 10 degree intervals between 60 and 100°F. I’ll use my Autotrickler to more precisely dispense powder charges. Increasing replicates from 3 to 5 and more precise powder measurement should significantly reduce error of the mean and permit greater confidence in the data.
     
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  19. daleboy

    daleboy Gold $$ Contributor

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    Wow,that was helpful...do it your way and don't stink up the OP's thread,some of us are curious and open minded .

    PS...Big words are not so tough,google them if you need to .
     
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  20. JEFFPPC

    JEFFPPC Silver $$ Contributor

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    You missed my point. This is a subject that is constantly being discussed. The only thing that matters is what shows on your target. No better way than to shoot in the extremes you compete in. I never see someone declare this is the answer and there is agreement from competitors that this is the answer. Case in point, VV133 in the PPC is always touted as being very temperature sensitive. New and different powders come out over the years that will be better, according to marketing. But when I look at what is being used at shoots in the PPC it's 50 to 1 VV133. So then the answer is always that it's used because shooters have a better handle on it. I agree, but it also applies to all the latest and greatest that come out. In spite of these discussions and all the marketing it all has temperature sensitivity that must be adjusted to if you want to be at your best. I appreciate the study the OP did but we are still left with.....it all has temperature issues even though I think many WISH for one that is not Has not happened yet.
     
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