.270 velocity variations

Discussion in 'Reloading' started by kstrick, Dec 8, 2009.

  1. kstrick

    kstrick Well-Known Member

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    I am using RL22 and RL15 and H4350 loading Win .270.
    I use the RCBS charge master, I prep my cases. I am using Berger bullets. I am being as careful as I can be with the whole process.
    I am not bench rest competition anal about it but I am very careful and consistent with my reloads.
    The problem is I am getting up to 100 fps differences in velocity in the same batch of reloads. I use a Lyman set of weights to check the scale. The weights have been verified with a commercial pharmaceutical grade scale. All that said...I trust the Charge Master scale.
    Any advice?
    I understand Retumbo is very consistent but I do not find any info for the .270. Has anyone tried it??
    Thanks
    Ken
     
  2. demented

    demented Well-Known Member

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    Not having much experience with Hodgon powders I can't specifcally lay blame to them being your problem. I will say that I have never seen this when I'm using IMR powders unless using something too slow for a particular cartridge. Also are you using the same primers for all loads? It may take some experimenting to find your problem.
     

  3. Fitch

    Fitch Well-Known Member

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    I also have an RCBS ChargeMaster. I was getting velocity variations and tried all sorts of things. In desperation I started weighing every charge, pour it out of the charge master pan into my balance beam scale pan. I discovered I was getting +/- 0.3g charge variations when the charge master said it was right on. Now I set up the balance beam with check weights, set the ChargeMaster 0.2g low and trickle to weight.

    ES (the statistic that matters for hunting) is down to under 25 fps most of the time.

    Fitch
     
  4. kstrick

    kstrick Well-Known Member

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    I am not mixing primers.
    I am not mixing brass.
    I check the scale with the weight set every 6-8 throws. It appears to be very accurate.
     
  5. Fitch

    Fitch Well-Known Member

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    Checking an electronic scale with check weights will only find gross errors, not the sort of problem you have. You have to check the whole process that leads to the quantity of powder you pour into the brass. The "only" way to do that is to weigh "every" charge on a good quality balance beam scale.

    The reason for this is two fold. First, electronic scales have a deadband (plus or minus tolerance) built in or they can't work. The size of the deadband required to allow the scale to settle depends on the quality of the electronics being used to read out the strain gage bridge that is the heart of the scale.

    My electronic scale always, every single time, gives me the right answer with check weights but it throws charges with an extreme spread of +/- 0.3g. The extreme spread in charge variation is what must be controlled. You have to weigh the charge that is thrown by the charge master to find thrown charge variation issues. Weighing check weights won't find the problem because they don't check the whole process including the dynamics of adding powder to the pan.

    Which leads to the second cause which is the process for metering the charge feeds powder to the pan in clumps as the weight gets clost to the desired final weight. The weight increases in clumps as powder dumps out of the tube. It is almost impossible for the scale to have a long run extreme charge spread smaller than than approximately plus or minus the largest clump size. That's just how it is. You get charge spread you get velocity spread.

    The two causes work together to create the extreme charge spread that happens with the ChargeMaster. If the final clump just crosses the threshold, the scale will stop the power trickler which is what the CM is and the charge will be on the low side of the deadband. If a clump falls on the scale that takes it to the upper end of the deadband, then the charge will be heavier. If the last clump was under weight but large enough to dynamically trip the comparator in the scale, the charge will be under weight.

    Electronics are fine but the low cost electronics in powder scales aren't all that great so they have a bigger dead band than laboratory quality scales. Near as I can tell, electronic reloading powder scales are the cheapest thing that marketing thinks will sell the product. That's just how businesses are run. The most profitable businesses are those where they are really good at barely getting by.

    The RCBS ChargeMaster is the best of the bunch near as I can tell, but it isn't nearly as accurate as trickling to weight on a balance beam. My balance beam isn't perfect, but checked with a borrowed very accurate laboratory scale (accuracy of +/- 0.02g) it demonstrated extreme variations under +/- 0.1g.

    Try weighing every charge as you reload - measure a hundred thrown charges. You will see more variation than you would ever have thought. I certainly did. The variation is the largest with big stick powders like IMR7828 and almost non existant with powders like IMR2460 (that looks like tiny shiny black ball bearings) that flow almost like water.

    There are lots of other things that can cause velocity variation. Primer hole flash, variations in neck tension, seating to just touch the lands so some bullets touch, some don't, variations in crimping if the bullet is crimped into the neck, variations on overall length, worn out barrel (throat shot out or huge chatter marks in the barrel which one would need a borescope to see), and so forth.

    Your problem is probably not caused by just one thing. Contributors will have an effect that combines by the square roof of the sum ot the squares of their individual contributions. As you fix the causes, the variations will be less and less, but might still be dissapointingly large if the remaining cause is a more major contributor.

    Fitch
     
    Last edited: Dec 9, 2009
  6. kstrick

    kstrick Well-Known Member

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    Thank you for your time in that response.
    What has been so frustrating is that my .243 loads are consistently 10fps +/- using the same RCBS dies/scales attention to detail.
     
  7. Fitch

    Fitch Well-Known Member

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    You are welcome.

    Are you using the same powder in the .243?

    Fitch
     
  8. Boss Hoss

    Boss Hoss Well-Known Member

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    Some powders will just vary quite a bit. When developing loads for my 1k competition rifles I use the Denver Instruments but the Charge Master works close enough.

    If you are leaving the unfired cartridge in a warm or hot chamber for more than a few seconds this will also contribute to your problem. Too many variables to go into here.

    Think you are barking up the wrong tree here imho.
     
  9. kstrick

    kstrick Well-Known Member

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    yep
    H4350 RL22 and Varget in the .243
    Thats why this whole thing is driving me nuts!!
     
  10. nheninge

    nheninge Well-Known Member

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    Things I think about for extreme ES...

    powder charge as has been discussed
    primers (use of benchrest primers has narrowed ES in my hands)
    neck tension- are you turning necks to achieve consistent neck tension?
    brass uniformity
    environmental factors (heated barrels etc)
    accuracy of chronograph
     
  11. kstrick

    kstrick Well-Known Member

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    I don't have a neck turner.....yet. I can see accuracy...but velocity?
    I have thought about the chrony...but how do you verify a chrony??
    I have been shooting bench rest primers. I got 5 bricks just before the crunch hit.
     
  12. nheninge

    nheninge Well-Known Member

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    Neck turning is a bit of a stretch, but I found that with necks turned to the same thickness, I was able to achieve the same neck tension on each bullet and I felt like the velocities seemed to be more consistent. To clarify, this was by neck sizing only without an expander ball on unturned brass. Probably related to different chamber pressures in the bullets with thicker necks and tighter neck tension??? This may or likely may not apply to you and also would only be responsible for small variation not 100fps variation as you describe.

    I have asked about chrony verification in the past with not much help. The only thing you can do is set two different models end to end and shoot over each (at the same time) to see how close the readings are with each shot. This gives you relative data (not absolute), but I haven't heard of a place to send in your chrony to have it validated. Don't really need to worry about this if your drop data matches your chrony's numbers. Sometimes the light here in New Mexico plays heck with my chrony. 100 fps might mean a difference in 20-30 inches at 1000 yards. If you are truly getting that variation it would certainly be evident at long ranges. Probably barely detectable at 100 yards?

    Lucky you on the primers! Hope to see an end to this shortage soon.
     
  13. steve99

    steve99 Member

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    I think you will find Retumbo is too slow burning to be an effective performer in the 270.

    Shot to shot variations in velocity can often attributed to certain powders in certain cartridges. Years ago I tested RE22 with 100gn bullets in my 243 and velocity varied by as much as 120fps. When I went back to H4350 shot to shot variations went back to a more acceptable 20fps-30fps.

    The same can be said when I tried W748 in my Marlin 444 - velocity was all over the place. Once I went back to H4198 velocity variations shrunk to single digits.
     
  14. kstrick

    kstrick Well-Known Member

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    Thanks for the advice.
    I have pretty much settled for H4350 for my .243 as well. I get consistent velocities as well.
    Thanks
    Ken