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Powder weight vs. volume?

Discussion in 'Uncategorized Threads' started by WNCRob, Jul 28, 2008.

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  1. WNCRob

    WNCRob Member

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    I'm having difficulty asking this question clearly...I would like to know if a desired ballistic result is more directly related to a powder charge's volume or weight? In a PW manual and in some powder companies manuals, it indicates an average weight of a charge for a specific bushing...I get approximately 1/2 grain less, yet ballistically, I get the specified results. I expect that in my case a low humidity environment (34% humidity on average) may contribute to a lower weight than in some other locales. As most powder companies recommend a specific weight in their reloading formulas, they leave it us to achieve the specified weight by finding the bushing that delivers that weight. Obviously, it is not practical for the powder companies to specify a specific volume as the measuring equipment is not generally available to the average reloader, so specifying a specific weight may be a compromise? I guess one would ask which is more repeatable? The weight or volume measure? So, is it best to weigh a specific volume and adjust the volume to the desired weight, or whether to stick with the factory-specified bushing for a given charge and ignore the weight? In this instance I am using Clays, which seems to meter rather consistently.

    Thanks.

    WNCRob
     
  2. Ahab

    Ahab Well-Known Member

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    "As most powder companies recommend a specific weight in their reloading formulas, they leave it us to achieve the specified weight by finding the bushing that delivers that weight."

    How much more specific do you need for instructions?

    Volume has nothing to do with the energy provided by gunpowder!!!!!!!!!!!!!!!!
     
  3. zzt

    zzt Well-Known Member

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    Actually, the correct answer is neither. WNCRob, powder manufacturing is not an exactly repeatable process. Every time each manufacturer creates a new batch (lot), it varies from previous batches. Sometimes by a lot, and sometimes by a little. The lots sold to Consumers for reloading are the ones that come closest to the "standard".

    So each lot of powder varies by weight and by volume. The weight per unit of energy varies less widely, so that is what manufacturers use to tell you how much powder to put in your shell.

    A bushing that throws 18gr of Clays one day, may throw 18.2gr the following day, and 17.8gr the day after that. It depend on the humidity in the air, and how exposed your powder is to it. Here is how I do it. If the new jug of powder is from the same lot as the previous jug, you don't have to do a thing. Just keep loading with everything the same. When I open a new jug from a different lot, I check to see if the bushing I was using for the old lot throws the same weight of the new lot of powder. If it does, no changes. If it doesn't, I change bushings until I get the correct weight. I use Hornady/RCBS bushings, so I have a wider range of choices than you do if you stick to PW bushings.

    Once I find the correct bushing for the new lot of powder, I use it for the entire jug/lot. The only adjustment I'll make is if the chrono tells me I'm faster or slower than normal. I don't change bushings up or down to "compensate" for more or less humidity, because humidity doesn't affect pressure or velocity. It is simply "weight" that doesn't count.
     
  4. chipking

    chipking TS Member

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    ZZT has hit it on the head. I weigh a new lot/Jug as soon as I open it and record the results in a Excel spreadsheet. This gives me a standard that I will load that entire lot/jug by.

    --- Chip King ---
     
  5. hmb

    hmb Well-Known Member

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    The weight by volume changes, but the energy by weight does not. HMB
     
  6. zzt

    zzt Well-Known Member

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    hmb, that is not what my chrono tells me. The last batch of Red Dot I bought required moving up two bushings (.006" larger) to throw the same weight, THEN increasing the charge weight by 0.5gr to maintain velocity.
     
  7. hmb

    hmb Well-Known Member

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    Change the batteries in your crono. There are a lot of variables at work here. HMB
     
  8. Old Cowboy

    Old Cowboy Active Member

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    Interesting question, and one I've pondered some myself?

    I suspect the reason that powder charges are specified in grains (weight) is that we all have an accurate means of measuring weight and a grain on my powder scale is the same as a grain on your powder scale is the same as a grain on the powder scale of the guy who made up the loading manual.

    Personally, once I've settled on a shotgun load I don't even bother trying to remember the weight..........my recipe just specifies the powder and the MEC bushing I use, like----29 bushing 700X,.........or----32 bushing CLAYS.

    If I felt the need to verify consistency with a new jug of powder I'd rather do it with a chronograph than with a scale.

    John C. Saubak
     
  9. phirel

    phirel TS Member

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    The weight per volume of powder differences would be less if we could drop a volume of powder that was all powder. But, in our bushings we drop a volume of powder mixes with a lot of air spaces in the powder. The amount of space taken up by the air in our powder volume measurements varies.

    If powder were a liquid, we could accurately measure it by volume. But, since it is little flakes of solid with air around each flake, weight becomes the most accurate way to measure it.

    Pat Ireland
     
  10. John Thompson

    John Thompson TS Member

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    Powder has a burning rate and a specific gravity. You obtain the weight of a charge by volume. Without going into the math, a .447 powder bushing diameter will throw 18 gr. of Green Dot, a 2 3/4 dr. equiv. same bushing will throw 700X at around 21.3 gr. way too heavy. Always measure by wt., never trust to a bushing chart as each lot of powder of the same type can vary in specific gravity.
     
  11. halfmile

    halfmile Well-Known Member

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    A single stage loader will drop more powder with the same bushing as a progressive.

    Manufactures lie just a little about their bushings. Lawsuit protection, ya know.

    Lot numbers will vary in volume/weight ratios.

    Winchester, Federal, Remmy, etc can adjust their machinery to utilize a certain powder perfectly, no matter if it isn't exactly to spec. The powders that we buy over the counter are much more tightly controlled, since most of us do not have the expertise and equipment the factories do.

    And with all that said, unless you want to go to the anal case inspection and prep that the rifle guys do, a half grain almost does not make a perceptible difference in shotgun shooting.

    There are many variables in gun performance, and the worst one is where I park my hat.

    HM
     
  12. wolfram

    wolfram Well-Known Member

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    The bushing charts can be relied on to get you close to your desired charge weight but most of us load a variety of components and begin each loading session by verifying charge weights with a scale. Thats my SOP anyway and I have caught mistakes in my bushing selection several times. These were the kind of mistakes that make varations in powder density seem trivial. The scale checks may add an extra 5 minutes to your loading session but it is time well spent.
     
  13. WNCRob

    WNCRob Member

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    Many thanks to everyone for their comments. I guess what started me thinking about this is that several powder/component company sites recommend a charge of ,say, 17.8 grains. The PW chart indicates that this weight should be produced by the J bushing. Well, the J-1 bushing produces 17.8 grains and the J bushing produces 17.2 grains. 17.8 grains produces a hotter load than the 1145 fps that I'm attempting to achieve, while the J bushing with 17.2 grains is right on the money. So, what's my observation? 17.2 grains of powder produces the desired result, not 17.8 as the "factory" recommends...and, 17.8 grains was recommended by several different factory sites. Confusing.
    Again, thanks.
    WNCRob
     
  14. John Thompson

    John Thompson TS Member

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    Are you making this determination with a chronograph?
     
  15. WNCRob

    WNCRob Member

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    I just spoke to Hodgdon about my perceived discrepancy in performance relative to the published stats by Hodgdon, Remington and others (i.e. that handloads with "factory recommended" charges are, in fact, hotter than their specs would seem to indicate). Apparently, when arriving at loads and performance stats, they use a barrel configuration as stipulated by SAAMI...this bbl is 30", "standard" bore, forcing cones, etc. Many modern bbls with wider bores, extended forcing cones, etc. will produce a somewhat "faster" result. So, the 17.8 grain load ("factory recommended" for 1145 fps) may well be producing "3-dram equivalent" performance in my Kolar.

    In light of this, I suspect that anyone with a "modern" bbl should be aware of this characteristic when developing loads, and that factory recommended loads may well be a bit hotter than their specs would otherwise indicate.

    WNCRob
     
  16. zzt

    zzt Well-Known Member

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    WNCRob, they also use a different type of chrono. If you are using a light operated chrono and a full choke, you can expect readings approximately 30fps faster than factory.
     
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