Pressure flats

Discussion in 'ELR, Ballistics & Bullets Board' started by tomswede, Jan 8, 2018.

  1. milanuk

    milanuk Team Savage Silver $$ Contributor

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    ...or a ladder test at distance ;)
     
  2. Berger.Fan222

    Berger.Fan222

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    I hope that is sarcastic.

    There are too many confounding factors at distance that render bullet drop an unreliable proxy for velocity. The shooter may not care whether the vertical tightening across a range of powder charges is due to velocity flattening or positive compensation, but a ladder test at distance cannot really be used to establish pressure or velocity flattening. You need a good chronograph and a statistically significant sample size for that.

    See: http://forum.accurateshooter.com/threads/positive-compensation.3890281/
     
  3. fredo

    fredo

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    I don't reference MV "flattening" so much as an indicator of an accuracy node, rather that it is another signal of that particular powder's velocity potential is close to peaking. In that regard, the only "flattening" of the curve that I take note of is that charge weight range is nearing the point of over-pressure & case damage/failure...
     
  4. retired

    retired

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    i do not know who berger222 is, i do know tom matt donovan and alex.
    i'll stick with their real life facts over someone else's math
     
  5. Berger.Fan222

    Berger.Fan222

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    The method some describe with a simple ladder test and a small number of shots can work well in the hands of experienced reloaders who combine careful component selection, brass prep, powder weighing, and bullet seating to reliably produce small extreme spreads in velocity for any given powder charge.

    But I've measured too many real F-Class and bench rest velocity spreads (LabRadar) to recommend that approach with much enthusiasm to a broader audience. Not everyone can effectively implement methods in the same way that the most expert and experienced reloaders can.
     
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  6. retired

    retired

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    and the volume of shooting recommended by you is impractical for the average shooter.
    the average shooter is not skilled enough for consistent loading and shooting.
    working with ladder data adds experience and improves the shooters skills.
    i like data, but the bottom line is real world shooting is what counts, ladder supports that.


     
  7. Berger.Fan222

    Berger.Fan222

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    Been practicing and teaching 20+ round load work-ups for over 20 years. My view is that beginning reloaders really need to load and shoot 5 rounds at each powder charge as they work up to look with enough care for pressure signs before incrementally increasing the powder charge. Shooting one round at a given charge is insufficient to gain confidence that there are no signs of excessive pressure before increasing the powder charge.

    I've introduced lots of new shooters to the sport. In addition to a bunch of average shooters, some of my more exceptional students have a combined 5 national championships, 5 second place finishes in national events, multiple cleans, two national records, and lots of victories in local and state events.

    Teaching a 20+ round load work up is not holding anyone back. We've found it to be very reliable for identifying the most promising loads in a variety of cartridges with a wide array of match, varmint, and hunting bullets. Slow is fast. Fast is accurate. Accurate is deadly.
     
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  8. CharlieNC

    CharlieNC Gold $$ Contributor

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    From my limited experience the target is more reliable than the chrono; in other words the SD of the shot (or group size if you prefer) vs the POI changes is less than the SD of the velocity as compared to the incremental changes in velocity due to charge weight. Not to mention the compensation due to harmonics can dominate the effect of the velocity deviations; isn't that really what we are trying to locate and harness as a node?
     
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  9. retired

    retired

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    so far all i have heard is you trying to justify your expensive process...a process you teach and i assume make money doing. so you have a vested interest in YOUR PROCESS. we ladder shooters are only interested in a personal progress, not filling our wallets.
    i have one national championship, lots of wins, over 40 years of learning how to do it "right".
    some how i managed without your 20 shot process.
    those who can, do
    those who can't, teach.
    you have a good day

     
  10. normmatzen

    normmatzen Gold $$ Contributor

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    I do believe it is not a myth. Our barrels have two distinct resonances. The first one is a linear resonance akin to an organ pipe. This is sometimes called the traveling donut. This resonance is a function of the speed of sound in the steel used for making the barrel and the exact length of the barrel. When the round is fired, a slight bulge goes down the barrel at the speed of sound in steel. When this bulge gets to the muzzle, it inverts phase as the barrel is open and becomes a constriction. When your bullet moves with an appropriate barrel time, when it gets to the muzzle about the time the traveling donut does, it slows down the bullet very marginally. at the load causing this effect, you will see a spread of loads where Mv is flat with load. So, at this load, the gun is less sensitive to powder lot and weight variations.
    But, there is another resonance which is the cantilever resonance where the barrel whips up and down (if your gunsmith clocked the barrel correctly) which when tuned correctly, alters the instantaneous angle of the barrel so there is a slight variation of Mv that puts the bullets in the same hole provided the change of angle sends slow bullets up and fast bullets down. That is positive tuning. If tuned for negative resonance, that Mv will cause splatter of your groups!
     
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  11. tomswede

    tomswede

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    Lots of interesting input. It seems to me that the “flat” is subtle but maybe it exists. It’s hard to imagine what causes it. Need to contemplate this a bit. For long range the SD needs to be low so chronograph data is needed for the chosen load. If shooting a ladder on a target, does trying to read the velocity increments add anything to what that target already says?
     
  12. milanuk

    milanuk Team Savage Silver $$ Contributor

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    Sorta my default mode... ;)

    In a more serious vein, it depends. You came across, or at least the way I read what you posted, as advocating 20+ shots. If you mean *per increment*... then yep, we're going to have to disagree. If you meant something else, please elaborate.

    Plenty of people have demonstrated that its very much possible to identify and tune to a 'flat spot' on target with a lot fewer shots per increment than that. I personally am uncomfortable with and/or have low confidence in doing a ladder with just one shot per increment, but that's based on my experience. Somewhere in there is a tipping point between 'enough data to be confident' vs. beginning to introduce un-necessary 'noise' from ambient conditions, shooter error, etc. And when I mean 'confident', I don't mean I'm submitting the data to a scholarly journal for peer review.

    Just in case it wasn't clear... I don't necessarily advocate 'run a ladder, and call it done'. I look at ladders as more of a sort of screening experiment, to narrow down the area of interest. I've seen various recommendations in texts on that sort of thing that suggest allocating about 25% of your 'budget' for this stage of your experiment/test. That sounds about right, by my experiences. Unfortunately there are times when I've 'spent' way more than that trying to 'make' a load work, when I probably should have just said 'enough' and moved on to something else more productive.
     
    Last edited: Jan 10, 2018
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  13. Berger.Fan222

    Berger.Fan222

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    No need for 20+ shots per increment. 3-5 shots per increment is enough to have a sense for what your velocity variations are at each point and whether the observed flattening is an anomaly or a real indicator of the response of velocity to increasing powder charge.
     
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  14. fredo

    fredo

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    I don't think anyone suggested that shooting 20+ individual ladder tests is the way to 'proof' a load. Rather that, a perceived 'flat spot' may not be as evident or pronounced when a larger sample size is examined...

    Reckon we can still agree that the target don't lie, and is prolly the most practical indicator of where a charge weight should settle at?
     
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  15. retired

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    i think you are mixing facts.
    ladder vs "Been practicing and teaching 20+ round load work-ups for over 20 years. My view is that beginning reloaders really need to load and shoot 5 rounds at each powder charge as they work up to look with enough care for pressure signs before incrementally increasing the powder charge"

    initial loads at 5 rounds is typically a waste of ammo. a 3 shot group never gets SMALLER WITH SHOTS 4 AND 5.
    latter he addmits to 3 shot groups, but that contradicts his "training plan".

    yes the target is the final answer.

     
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  16. damoncali

    damoncali Gold $$ Contributor

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    There is a difference between five individual 3-shot groups and five 3-shot groups that vary a single variable with a known behavior. The latter is what we're discussing here.

    I really don't understand the aversion that people have to shooting in order to gather data. Is it not practice? Does it not increase your experience? Nobody bashes practice or experience, but the second you recommend that statistical confidence is a good thing, the math haters come out of the wood work. Whatever works, I suppose. Different strokes for different folks.
     
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  17. Berger.Fan222

    Berger.Fan222

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    Exactly. The only way you know for sure you have a load capable of shooting a 200/200 is to shoot 10 shots and put them all in the 10 ring at distance. Then you start trying to increase the X count. 200-10X to 200-15X to 200-20X. But you gotta shoot 20 shots to know for sure what the X count potential of that load really is.

    All the load work up techniques attempt to reduce the time and effort to get to that point. But in the hands of different reloaders, art gets mixed in with the science and all the details of brass prep and projectile sorting and so on suddenly matter, so my art might be different from your art.

    Even with 20+ shots of load work up, all I ever know is that a load has promise. Until 20 shots are on an F-Class (or another appropriate) target at distance, I still don't really know.
     
  18. retired

    retired

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    so the question is part of the problem.
    no discipline is referenced.
    a hunter can test with 3 shot groups.
    a short range br shooter with 3 and 5's
    20 rounds only apply to prone/position shooters..a narrow world
    long range 600/1000 shoot both 5 and 10 but not 20.
    elr is short strings from 2 -3... kof2m does 5
    soo generic questions seldom see a specific answer.
    i'll stick with ladders.

     
  19. Meangreen

    Meangreen

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    I don't mind shooting larger round counts to be statistically confident in what the load will actually do. I also don't follow Audette's method of starting 20 increments below maximum. There is a very narrow range of performance I am looking for. I couldn't care less if there is a big node 4 grains below max charge.

    I am looking for a high node within more like 1 or 2 grains of max. If these don't show significant promise, I move to something else.

    Shooting 10 shots or more at a single point of aim will show you what is going on harmonically with your barrel in the shape of the group, in addition to the velocity data you are gathering.

    I also shoot most groups these days at 200 yards. At this distance, you get enough separation to actually see any stringing very clearly, yet it is close enough that any environmental elements can either be controlled or easily accounted for.

    I'm gonna get hammered, but there it is.
     
    Last edited: Jan 11, 2018
  20. rhovee

    rhovee

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    I am new to the Forum and have found myself in the deep dark hole of reloading. I have been trying/reading different load development techniques that work. Ladder, OCW, 10 shot load development, and asked Alex tons of questions!. I shot my first ladder a few months ago over a chrono. It was happen stance that i ended up with .9 grain difference in powder charge that had 1/2" vertical at 350 yards over 3 shots with 5 FPS difference. However, when i took my next shot the speed was the same and the POI jumped 5" vertical. This tells me that you can't always just base loads of velocity. I went back and shot (3) shot groups in the node and it wasn't as wide as it seemed on the chrono. I ended up with .4 grain difference in my load. But there was a total of 1.2 grains that had an ES of 5. This is a hunting rifle.
     

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