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Determining Powder Drop Variance?

Discussion in 'Shooting Related Threads' started by mrskeet410, Oct 31, 2009.

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  1. mrskeet410

    mrskeet410 TS Member

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    I read at this site posts from those that claim they get powder drop variances of +0.1 to -0.1 grains. How are you measuring that?

    I'm interested in how you determine that range. How many samples? When do you sample?

    This post isn't about how you get the low variance, e.g. Red Powder Baffle, anti-static tissues, grounding reloader, etc, that's a difference debate. This thread is about you determine your variance?

    Please be specific.
     
  2. rick979

    rick979 Active Member

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    I weigh the first 3 shells when the powder bottle is full then weigh again at #15, #16, #17. Then when powder bottle is 85% depleted I weigh 3 more shells in a row. My machine seems to always throw within .10 grains when I don't make a reloading mistake. Variance of one tenth of a grain I consider to be perfect.
    Rick~~~Texas
     
  3. slic lee

    slic lee Active Member

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    I drop powder at the beginning for 4 shells, I make a shell on the 5th and weight it, if it comes out to the .1 its good, it always stays every 15 or so I check again.
     
  4. short shucker

    short shucker TS Member

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    I get my consistant drops with a couple of 366's that are about 15yrs old. I keep a steady smooth pull and release. I could also do it with a Mec when I used one of them.

    I generally sample 5 to 6 shells in the first 25. Then spuradically from there. No real set shell number, just a random sampling. I probably check 10 to 12 shells per 100. I would do it more, but 366's aren't the easiest to remove hulls for checking.

    ss
     
  5. mrskeet410

    mrskeet410 TS Member

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    Rick and slic Short - What type of powder?

    Shot - What variance do you get on the random samples?
     
  6. short shucker

    short shucker TS Member

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    mrskeet410,

    Hodgdon products mainly. Titewad, Titegroup, Universal Clays, and Longshot.

    One of my shootin' buddies gave me a pound of promo to play around with. I'll see here in the next couple of weeks how that meters.

    I don't ever check my shot charges unless I get a new bushing. Those 366 shot bushings are dead on the money. If the shell is off a pellet or two, it won't change whether or not I break the target.

    ss
     
  7. miketmx

    miketmx Well-Known Member

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    I have an older PW900 loader without the handy cutoff features so I have to cut open a shell to check the powder drop. I use Red Dot and Green Dot which are bulky flake type powders and when I periodically check the powder drops, they are usually within 0.1 grain of my last check. PW loaders have a baffle in the bottom of the powder and shot tubes so that weight from a full bottle is not an issue.
     
  8. Neil Winston

    Neil Winston Well-Known Member

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    I just take a shell out now and then. With my Mec it's easy, just take it out of station 3. I use an electronic scale and usually get about what I expect. Some I shoot in a chronograph just to make sure.

    I found that the best chronographs can just start to differentiate charges varying by 0.3 grains if you shoot maybe five or ten and average them.

    Shells I load on my RCBS combo dispenser/scale are within about 0.1 grain. If I load ten to that standard then ten on my MEC 900H and test them through an Oehler 84 inductive chronograph I can't tell them apart. My MEC can match shells loaded to 0.1 grain, though its powder drops are more variable than that. That means that there are other sources of variability which are greater than than caused by (minimal) powder-drop differences.

    That's why I don't worry if I get a powder weight a little more or a little less than I expect, say 0.3 grains either way. Mostly I don't get such a difference, but sometimes I do.

    Neil
     
  9. JerryP

    JerryP Active Member

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    By taking a shell out at random and checking, but I don't normally like to stop the loading process and check. That just invites more variance and other screw ups. I don't think .1gr is realistic overall, regardless of machine or powder. .2gr is more like it. That could be a difference of .4gr. among shells.
     
  10. Quack Shot

    Quack Shot Active Member

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    I run about ten drops through to settle the powder, then check five individual drops. I then run another ten and check another ten individual drops. I then drop ten more into one pile and weigh that and get an average. I do that with a full bottle and then with one about half full, or half empty, depending on whether I'm optimistic or pessimistic that day. I'll check one drop about every twenty shells or so, just to be sure. When my variances are +/- .1 grains, then that's my variance. If it's a bit higher, then that's what it is. This is basically what I do when I open a new jug of powder. I usually check three drops after droping five or more, before beginning my loading session, once I've determined what that lot/jug of powder is doing with a particular bushing. I'm not looking so much for the variation, but to get a good average and an idea if the drops are consistent enough for my personal standards. That would be around +/- .2 grains with most powders, or less than .5 grains of spread from high to low. Most powders do much better than that for me. Some powders like 800-X are near the limit.
     
  11. mrskeet410

    mrskeet410 TS Member

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    Neil - This is some good info. Thank you.

    "I found that the best chronographs can just start to differentiate charges varying by 0.3 grains if you shoot maybe five or ten and average them.

    Shells I load on my RCBS combo dispenser/scale are within about 0.1 grain. If I load ten to that standard then ten on my MEC 900H and test them through an Oehler 84 inductive chronograph I can't tell them apart. My MEC can match shells loaded to 0.1 grain, though its powder drops are more variable than that. That means that there are other sources of variability which are greater than than caused by (minimal) powder-drop differences."

    One question. Am I reading this correctly, i.e. that fired over a chronograph, your reloads from the higher variability MEC match the reloads from RCBS combo dispenser/scale?
     
  12. rick979

    rick979 Active Member

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    Mrskeet410: In answer to your question I load Solo 1,000 and Green dot powders. Also I probably cut up more shells than most folks as they go into a "questionable" stack if I think they may have a problem. Often the ones that I am dubious of have a cocked wad or poor crimp but even on these shells the powder drop is amazingly close. I agree with Neil that plus or minus a couple of tenths is probably not worth worrying about. I wish my shooting was as consistent as my powder drops bu it is NOT. Rick~~~Texas
     
  13. Neil Winston

    Neil Winston Well-Known Member

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    Mrskeet410. You asked about the variability of shells when fired over a chronograph. Do my MEC loaded ones (with a powder variability of -say - 0.2 grains plus or minus) look about the same in a data book as my one-by-one RCBS product with no measurable variability in powder? The answer is yes; you can't tell them apart when shot though an industry-standard chronograph.

    But speed variability is a tricky subject. My thinking is that good shells all have an irreducible variability whose average is such as to give an SD of eight or ten or twelve. But there is a considerable range of SD values they can take in producing that mean.

    You can shoot ten which are almost all the same, producing an SD way down at 3 or 4. But if you re-test, you will get 10 or 12. Or 12 this time will jump to 6 the next. Some of this is just regression toward the mean, but "stacking tolerances" probably plays a role too. The rest is just chance variability.

    But the rifle shooters have a saying "Good groups sometimes repeat; bad groups _always_ repeat" and that goes for shotshell speed variability too. I doubt there's a bird in a thousand in it, but some popular reloading parts just never work right. They have high SD'd when you start and never get any better. I use other products and no, I won't say what I avoid since I know it's possible I'm consistently making some mistake when I use them, but I doubt it.

    As I said when I started, if you get powder drops which are pretty close, that's the best you can do and doing better won't change a thing.

    Neil
     
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