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recalibrate powder scale--How often

Discussion in 'Shooting Related Threads' started by dhip, Jul 11, 2010.

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  1. dhip

    dhip Active Member

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    Just wondering,sure it's been answered before.How often do you recalibrate your powder scale?

    Reason I'm asking is I got a small shock today.I have had a pocket digital scale for a while ,but never used it. I use a rcbs(i think) scale and have been using it since I started reloading this year.Today,I figured why not check them together.I thouht I was throwing a light 1oz. load.rcbs scale was measuring 18.5.When I checked with digital,it said 19..So I recalibrated rcbs to read the same.yesterday in the rain the rcbs was measuring 18.8. I use grenn dot and after checking alliants chart I'm still in the safe range but not as light as I thought.I have a mec ,using the 32 bushing,and by their chart, it should be throwing 19.6grains.I was thinking today of dropping down a bushing,I's rather error on the light side.

    Thanks for any input

    Doug H.
     
  2. stokinpls

    stokinpls Well-Known Member

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    Let's take the easy one first. Your MEC bushing chart is only a yardstick table. The 32 bushing was throwing 19.6 grs.of Green Dot on the day the chart was tabulated, but with each new lot of Green Dot the amount a 32 bushing drops will likely change. You choose a bushing that looks like it's what you want, but YOUR SCALE is the final word as to what is going to end up in your hull.

    Assuming the RCBS is a beam balance scale, the only calibration you can do is to set the zero. After the zero is set, you can only check calibration by using test weights of known weight values - if you don't have any test weights, match bullets can be used in some cases.

    Assuming the digital scale is giving the correct value is another bad idea. What did you use to check the calibration on the digital scale? Again, if you don't have any test weights you're just guessing.

    " So I recalibrated rcbs to read the same.yesterday in the rain the rcbs was measuring 18.8. " If you mean the volume powder was weighing 18.8, the difference from the 19 of the day before could be bushing drop variation. Powder drop variations of 0.5 grains ARE not that unusual.

    Don't get flustered by this. You're at least using a scale to check your powder drops. That alone is a big jump in quality control. I would go back and follow the factory recommended method of "calibrating" the RCBS, then check it with some known weights (maybe one of your friends has some?). Once you have the RCBS checked out, try the test weights on the digital scale. If the digital scale checks out, then decide which scale you want to trust in the future. You're close to figuring it out, you're learning, this is the fun part. Good luck.
     
  3. slodsm

    slodsm Member

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    I check drops every time I am about to load up a large batch of trap or 5 stand loads, you results are about typical of my variance from the MEC chart and the actual weight. All of my drops on an "average" day of 76 degrees of AC will be about 1 bushing size lighter than what the MEC chart says they will be and they can vary up or down .2 from full to the refill line.

    I would suspect MEC purposely set up their chart like that so people who won't use a scale won't try an actual max load, go over, possibly boom, possible liable lawsuit, etc.

    Jeremy
     
  4. slowdp

    slowdp TS Member

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    Most good digital scales come with a test weight or two. That should be a clue. Digital scales are prone to change due to the many electronic components and metal fatigue of the load cell. The digital scales used for reloading are the cheapest of the cheap.

    Use the test weights often to double check the digitals. Like noted above - a good match grade bullet is a close substitute for a test weight.

    Another problem - digital scales can become non-linear. The weight may be accurate with the supplied test weight but very inaccurate at the low powder weights we are dropping. My digital was supplied with a 50 and a 30 gram weight for calibration and testing. Thirty grams is 462.972 grains. Calibrate with the test weight and then check a small match grade bullet (60 or so grains) to verify the accuracy at the low end. Now throw 3 drops of powder and weight them. The drops should be in the 60 grain area. That will give you confirmation of the powder drop in the range of the bullet test weight but only an average confirmation. At any rate, with all of this checking you should be able to trust the 20 grain powder drop measurement.

    Trust the old beam scale. Balance the old beam scale and test it for accuracy. The beam is slow to use but much more accurate, linear and repeatable than the digital. Once everything is verified for accuracy you can use the beam scale to verify the digital from time to time.

    Be very careful with your scales - especially your digital scales. Keep the scales covered when not in use so stuff does not drop on them. Work with the scales gently. Harsh treatment will blow the load cell or cause the scales to shift calibration.

    Never take the reading of the scale as being correct unless you have confirmed the reading by testing.

    Trust me on this - I stayed at a Holiday Inn Express last night - Don (the scale slut)
     
  5. Quack Shot

    Quack Shot Active Member

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    Don't use the bushing charts as gospel. They were usually developed using a single stage loader. Progressive loaders will usually throw light compared to the charts. Not unusual. Always use a scale to verify your drops. Also, get a set of check weights for the scales. I'd believe the RCBS scale before a "Pocket" digital. Don't try to "Adjust" your scale, except for zero. If it is way off, check with the manufacturer or a company that does that sort of calibration according to established standards. A set of Lyman check weights can be purchased for around $25 from someone like Midway-Usa. <a href="http://www.midwayusa.com/viewproduct/?productnumber=212586" target="_blank">Click Here!</a>
     
  6. Unknown1

    Unknown1 Well-Known Member

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    When a battery powered digi-scale starts to wander or becomes inconsistent, change the battery not matter how good you think it is.

    When you get tired of changing batteries in wandering digi-scales, buy a beam scale. As long as gravity remains constant and the scale remains clean and in one spot, it will remain reliable and repeatable.

    MK
     
  7. dhip

    dhip Active Member

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    Thanks for replies,I do check drops often,and just decided to check scale as another means to insure accuracy.Now,where could I get these check weights,especially in the grain size.One scale I have only does grams,not grains,and naturally it's the one that came with weights.After thought,rcbs scale was reset to zero by instructions,not actually adjusted to digital read out.After the zero adjustment it read almost the same,digital still tended to read heavier..I.E. rcbs scale read 18.8gr--- digital still read 19gr.... guess I'm getting a little anal about accuracy,but being new to reloading,I want NO accidents caused by my reloads.

    Doug H.
     
  8. Quack Shot

    Quack Shot Active Member

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    Check my post above and hit the link that says "Click Here!", or hit the one below.



    <a href="http://www.midwayusa.com/viewproduct/?productnumber=212586" target="_blank">Click Here!</a>
     
  9. Ahab

    Ahab Well-Known Member

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    Quick and cheap test weights ... new dimes ... 35 grains each.
     
  10. Hap MecTweaks

    Hap MecTweaks Well-Known Member

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    Ahab, you robbed me of a $.10 cent post! :)

    I use the weights that came with my old balance beam scale to test on the heavy side,new dimes and bullets I've kept for years to double check the accuracy. My old Lyman Ohaus 1005 has never failed me in weighing accurately.

    One of the first shooting trophies I won when I began shooting registered targets in 1970. It's a Timex!!

    Hap
     
  11. stokinpls

    stokinpls Well-Known Member

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    If you can find someone with a calibrated and verfied (with test weights) scale you can make your own test weights out of washers or chunks of metal. Just weigh them on their scale, write the values on them and head back to your place to check yours out. If you like them to be even numbers, better take along a file. Once you have a couple, checking calibation will be fast and easy. If your scale is any good at all, and no one fools with it, it should hold calibration for months. My PACT has never needed re-calibration though I've done it a few times so as not to get rusty. Good luck.
     
  12. cubancigar2000

    cubancigar2000 Well-Known Member

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    I have lots of calibration weights but this is the first time I ever heard of using a dime? I just checked a dime and it is right dead on 35 grains. Pretty cool. Sometimes we miss out on the most simple solutions in life, that is one of the reasons I like TS.com. Thx Ahab and hap
     
  13. timb99

    timb99 Well-Known Member

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    Bullets from reputable bullet manufacturers are usually very, very close to the advertised weight.

    I test calibrate my cheap little Frankford Arsenal scale with the test 20 gram weight, just about every time I switch it on.

    I periodically test it against my Lee balance beam scale. So far, so good.
     
  14. kiv-c

    kiv-c Member

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    Digital scales are easily affected by temerature and barometric pressure changes. Plug it in and let it sit for at least an hour, then run the calibration routine. Check it often after that, too.
     
  15. wolfram

    wolfram Well-Known Member

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    I got my first electronic scale for christmas last year and I like using it. The scale came with a couple of check weights and so far it has been dead on everytime I check. More interesting is that my old RCBS balance beam scale that I started out loading with in the 70's is right on the money as well. For some reason, I doubt that the new electronic scale will provide near the years of service that the old balance beam has.
     
  16. BDodd

    BDodd TS Member

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    Moving the balance beam scales from one end of a bench to another or a new spot near where you usually have it can affect it's accuracy. One should check it's accuracy with a known item or "check weight" any time it's been moved from place to place.......breakemall....Bob Dodd
     
  17. Ahab

    Ahab Well-Known Member

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    A balance beam scale will have an adjustment screw to level it. An off level scale will not real true.

    Set it to zero and if the indicator is not on the mark, adjust the level with the screw. Then place a known weight in the pan and if it is off ... there is an adjustment nut at the end of the beam to make the correction.
     
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