Charge weight vs volume, in filled cases - mind blowing discovery?

Discussion in 'Reloading' started by Max Heat, Feb 17, 2014.

  1. Max Heat

    Max Heat Well-Known Member

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    This sprang up out of another thread. In the interest of not hijacking THAT thread, I have started this new one.

    Quote:
    Originally Posted by Max Heat

    Lets start out by being in agreement that the closer you are to having a 100% filled case, the more efficent, in terms of velocity vs powder charge, the round becomes. From what I have found when working at (or very close to) 100% capacity, a change of say, 1% in the case-filling VOLUME of the charge makes MORE of a difference in velocity than a 1% change in the charge's WEIGHT! I have discovered that when using cases having randomly varying weights, the velocity spread will be considerably tighter if the charged is measured by dropping a marked or scribed rod into down into the case and perfectly matching the height (relative to top of the neck, so case lengths must match) level of the charge in each case, rather than by perfectly matching the weight of each charge. Does this blow your mind? But such measurements are only accurate enough when the case is filled to top of shoulder/bottom of neck minimum. This method appears to effectively negate variations in velocity caused by case weight (and thereby internal volume) differences.

    Now that I have gone public with my theory, for which I only have a small amount of supporting data at this time, I welcome anyone to try replicating it, and either concur (agree) or digress (disagree) that this is indeed the "case"!


    Quote:
    Originaly Posted by DocB

    Consider my mind blown!

    I can see the validity in your method. It is a very interesting technique.

    What do you use for a rod that's small enough not to displace the volume of the case?

    DocB


    Quote:
    Originally Posted by Max Heat

    The rounds were 7mm rem mag, and the rod was the one used to knock the case out of the sizing die and seat the primer, on a "Lee Loader" reloading kit for that round (referred to by Lee as the priming rod).

    The theory should apply "across the board" however, to ANY round. But the larger the diameter of the rod, without it being so tight in the neck that it's free movement might be restricted, the more accurate the volume measurement will be. It also needs to be a measurement that is "within" the neck, for maximum accuracy of the measurement. So we ARE talking no less than FULL cases, for the technique to achieve the maximun result. Filling the case is simply matter of finding exactly the right powder. Also, the finer the line is that is marked on the rod, the more accurate the measurement will be. That's why I mentioned "scribing" the rod.

    There IS a "variable" that could prove difficult to keep under control though. And that would be the "settling" factor, which obviously could have detrimental effects on the consistancy of the "true" volume of powder that is in the case. So absolute consistancy in the way each case is loaded & handled, will go a long way in assuring that the technique will work to it's full potential.

    One factor that I have given some thought to (but not tested as of yet), is how the weight of the measuring rod might affect the settling factor. The rod I was using is steel, about 5 1/2" long, and almost large enough in diameter to completely fill the ID of the case neck. I don't know if a rod that is made of a light weight material would offer more consistancy or not. It could be that the weight of the steel rod might actually HELP to equal out any case-to-case settling differences - I don't know.

    PS - I will admit that I did stumble upon this "discovery" purely by accident. If I hadn't been chronographing those shots, I would never have known.
     
  2. Mikecr

    Mikecr Well-Known Member

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    It's a good observation but you're missing a variable/correlation in matched case volume.

    What you're seeing falls inline with my contention that brass weight in no way correlates to actual case volume, which matters most to load performance due to load density at a given charge weight -and this side of 75Kpsi loads.
    In other words, if we're to use charge weight for consistency(instead of your rod), we need to be paying attention to actual case volume(H20 capacity), and NOT brass weight.
    With this, and consistent powder charging, load density should measure well with your rod.
     

  3. Mikecr

    Mikecr Well-Known Member

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    ADD: Some of this is of course dependent on case design and load density also.

    If you want PROOF of density over powder or brass weight try this experiment:
    Chamber a round with the barrel pointed up and slowly lower to a rest. Note the velocity on firing.
    Now chamber a round with the barrel pointed down, and slowly raise to a rest. Note the velocity on firing.
    The lower your fill, the greater the difference, regardless of same powder and brass weight.
    You'll see the same from cases weighing the same, and charged the same, but of different H20 capacity(affecting load density).
     
  4. Max Heat

    Max Heat Well-Known Member

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    More info:

    When I was using that method, which was between 1 1/2 and 2 years ago, the charge weight in the 7RM case was around 75gr of Reloader 19 - definitely a hot load. Bullets were Nosler 120gr ballistic tips. I haven't located the sheet with the actual chrono data on it yet. At the time, I do remember posting something to the effect of: "80% of the shots were within 5fps of 3680". I remember thinking that was pretty amazing , as I never saw such a low ES in ANY of my chrono data prior to that.

    I haven't shot the RM since then, as my attention has shifted to the 7RUM, which I purchased not long after that. But now that I am settled on a powder that makes use of the full case capacity of the RUM (RL33), I am in a position to gather similar data. But with the local range now closed due to all of the snow that has been piling up around here recently, it may be an unknown amount of time until the testing can comence.
     
  5. MagnumManiac

    MagnumManiac Well-Known Member

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    I would also like to add that with my own experimenting wth case weight and case capacity, that the differences in case capacity were far less affected if the charge density, or put in other words the packing scheme of the case over actual charge weight variations made more of a difference to low ES and SD numbers. I used a 'swirl charge' technique of getting the powder to settle to the same height in the case by tilting a powder funnel and pouring the powder into the case so that the powder swirled around the axis of the funnel and made the powder settle into a denser column, as compared to being just dumped by the measure. The difference was substantial between 'as dumped' from the measure to being 'swirl charged' by the funnel.
    Variations in velocity were dramatically reduced and the load was easier to tune with less rounds fired down range. It appears to work best with compressed loads, either heavily or mildly compressed slower powders have the largest differences.

    Cheers.
    gun)
     
  6. varmintH8R

    varmintH8R Well-Known Member

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    Interesting thread. If volume is driving the performance, would a typical powder throw give you the same result without measuring using a rod in the case? It basically fills a chamber of known (set) volume and dispenses it when flipped. Any measure with a baffle should keep any "packing effect" to a minimum.

    Maybe worth adding this method to your testing and see how it compares.
     
  7. Max Heat

    Max Heat Well-Known Member

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    But the thrower's set volume, which does not vary (once set), is intended to represent a set weight. What I'm talking about is using each case's own volume to dictate exact amount of powder, who's weight is allowed to vary [slightly] from case to case, maintaining a consistant fill level of the case.

    At that time I saw those amazingly close chrono #s, I didn't have quite as much equipment to work with as I have now. I've been loading my RUM rounds individually by weight, searching for the optimum powder type & charge weight. But now that I've settled in on the powder, and almost narrowed down to the exact "base" charge weight that I want to go with (right around 102 or 103gr, which IS into the neck of the case), I'm going to have the powder measure attached to my progressive press to drop a charge into the cases. Then make final tweaks to each charge, according to readings from my "powder cop" die, before sending the cases on to the seating station, and out.

    The powder cop does actually have a rod that "drops" into the case to allow visual verification of the charge level, before it moves to the seater. If the charge level is up into the case neck, the rod measurement will be roughly 5 times more accurate than a similar measurement would be if the charge level is below the shoulder. The rod uses an o-ring for reading the charge level. I think more accurate readings could be taken [and therefore finer adjustments possible] if a small, very thin washer [of appropriate size to fit the rod] is placed on top of the o-ring, with something of equal thinness that it can be lined up with.
     
  8. varmintH8R

    varmintH8R Well-Known Member

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    I promise I am not trying to be confrontational:D. I am very interested in the result of your testing (and if we ever see bare ground here again, hopefully I can contribute).

    By design, a throwers set volume is just that - volume. Weight is a function of the thrower's chamber volume, and if weights happen to be similar it merely represents a consistent bulk density of the given powder.

    I agree that measuring relative to actual case volume would introduce another variable that could be meaningful. With no data to back me up (prove me wrong!) my first thought is that the resolution of a rod measurement would be too course to measure the relatively minute volume changes between cases fired in the same chamber. This would be especially true of extruded powders, where granule orientation will effect bulk density significantly.

    I'm interested to see how this pans out.

    Brandon
     
  9. Max Heat

    Max Heat Well-Known Member

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    I agree that the case-to-case variations in internal volume probably ARE very mynoot. And it really doesn't seem to make sense that eyed-up powder "level" readings could possibly be accurate enough to compensate for those variations. The unexpectedly tight chrono numbers did get my attention though. But it's possible that maybe I did jump the gun, in drawing conclusions from too little data, which I can't even locate now to post up. Without even having those actual #'s to back up what I am saying, it doesn't put me on very solid ground.

    So it looks like time to stop saying, and start doing. The best thing to do would probably be to exactly replicate what I did, and see if the #'s come up similarly. But being that I'm more into shooting the RUM now, I'll see if THAT gets the results that I'm claiming. Only failing that, will I fall back on an exact replication scenario, using RM rounds. With how deep the snow has been getting around here lately, it will probably take at least a few days to a week (possibly even longer) until I can get back here and post some #s. But I WILL definitely do it.
     
  10. TracySes23

    TracySes23 Well-Known Member

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    I've read on a few occasions over the last 30 years or more, that a powder measure dump (my terminology) will give the same volume & hence excellent accuracy. I've always had a problem with that, but I've never attempted to disprove it. The reason I have a problem is because if I bump the stop a time or two it will often throw a different charge weight. If I don't bump the stop, but instead slowly bring the arm to the stop, I still get charge weights that vary. Some powders simply don't settle well.
    Perhaps my logic is faulty, but I have a heck of a time trying to justify using varying charge weights just because the dropped charge came from set volume in my powder measure. Laziness & the thought of wasting components ($$$) keeps me using dumped charge weights as close as possible to being the same.
    I've had only one (modified) Herter's powder measure that deviated from this & only when I used certain powders such as pistol powders or very short grained cylinder, tubular powders or ball powders. I had fabricated a micrometer adjustable cylinder for it which had a slightly larger ID than the one that was original. However it didn't work well with coarse grained powders.
    I gave it away & wish I hadn't. I still weighed each charge, but rarely had to trickle in more powder. I might give the "indian giver" routine a shot.
    I concluded there is an optimum ID for different powders.
     
  11. Timnterra

    Timnterra Well-Known Member

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    This is a very interesting thread. Are we just talking about achieving optimum velocity and efficiency for a given case or does the volume also play into accuracy?

    Has anyone toyed with the idea of removing the airspace left in the case with a filler? I'm thinking of the cream of wheat fire forming method being employed to top off a case with a less than full powder charge. This however sounds counter productive because it would seem (I assume) as if you were firing a bullet weighing the combined weight of the creme of wheat and the bullet. Sounds like a recipe for dangerous pressure. Just a thought
     
  12. HarryN

    HarryN Well-Known Member

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    In other industries, such as epoxy and paint mixing, they often use vibration to help settle and mix powders for improved consistency. The results for those applications is quite substantially affected by the frequency, amplitude, and direction of the vibration, but part of this is due to the difficulty of some of their mixes.

    I am just guessing here, but perhaps some simple method of vibration or rotation could be used to help improve the powder settling / charge density.

    The part I am unsure about though, is you would want to be really careful that you don't start breaking up the powder into dust or that could really mess things up.
     
  13. Outlaw6.0

    Outlaw6.0 Well-Known Member

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    Please, Please don't do that. COW works great for fireforming WITHOUT a bullet seated in the case. However, there is a gentleman from here in town who tried COW in a 6.5-06AI with a 140grainer seated on top of it. He lost his right eye & thumb (IIRC) & has a titanium plate in his skull. That Rem700 detonated like a frag grenade....

    COW (or any filler other than powder) does not burn, you are basically tripling or quadrupling the mass of the projectile you intend to send down the barrel. Add to that the fact that the mass inside your case is larger than the neck due to the bottleneck design; it is not a question of if it will blow up in your face, I promise it will.


    t
     
  14. Timnterra

    Timnterra Well-Known Member

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    Wow that is awful! I'm glad you posted that!