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I don't think my scale is accurate

Discussion in 'Handloading and Reloading' started by ny32182, Feb 21, 2008.

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  1. ny32182

    ny32182 Member

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    I have an RCBS Rangemaster 750.

    I calibrate it per the directions and using the check weights, which are 20 and 30 grams.

    Once I zero it out, the check weights weigh 20.02, 30.03, etc.

    After some calibrations, the check weights will weigh 20.03, 30.04.

    My 68gr match bullets are weighing 68.2 after one calibration. 68.3gr after another. Etc.

    Help...
     
  2. ny32182

    ny32182 Member

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  3. moosehunt

    moosehunt Member

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    It appears that your balance is pretty accurate, but the precision may be off. But, are you dead sure your check weights are precise? How many different times did you weigh that 1 bullet? Do you know the precise weight of the bullet? What degree of precision and accuracy is the balance supposed to produce? You may be there, but until we know those answers, can't say.
     
    Last edited: Feb 21, 2008
  4. ny32182

    ny32182 Member

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    First, I don't know if the check weights are accurate. For now, those have to be the gold standard by which the system is judged.

    If the scale is calibrated using those two weights, then no matter whether they are perfect or not, they should at least be a reference point, right? So if I calibrate with a 20 gram weight, and then the same weight weighs 20.02 or 20.03 grams a couple minutes later, I have a problem, right?
     
  5. ny32182

    ny32182 Member

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    I recalibrated the scale, pulled a couple bullets from the loads I was just working on, and measured 23.4gr of powder. When I loaded them, it was measuring 23.5gr.
     
  6. Crimp

    Crimp Member

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    Do you have a balance scale that you can compare your measurements with? Or a friend's scale you can weigh your check weights on?
     
  7. ny32182

    ny32182 Member

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    Unfortunately, no.
     
  8. Ridgerunner665

    Ridgerunner665 Member

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    I had the same problem with an RCBS 505 scale....it weighed .2 heavy, RCBS sent me a new one without any hassle (on their dime), it still varies by + or - .1 buts its close enough for pistol rounds. For my rifle rounds a friend is letting me use one of his scales...its a better (more accurate) scale than any I've seen...he has a small printing company that prints on mylar with powdered ink (VERY expensive ink)...he uses these scales to measure his ink samples (I got his spare). Its just a digital scale a lot like any reloading scale...but a tad more expensive.
     
  9. DJW

    DJW Member

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    My RCBS scale is supposed to be "accurate" within + or - .1gr. Sounds like yours fluctuates in that range.............I seriously doubt that variation will cause you any real problems in accuracy or safety.
    Best, DJW
     
  10. Idano

    Idano Member

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    If you are using the AC adapter try it with only the battery. It is possible there is too much noise on the line and it is interfering with the calibration. I have a Cabela's Model EG1500 Reloading Scale, which I suspect has the mother board as your's the , PACT, Hornady, Dillon and all the others of that style and in my reloading room can only run it with the battery because the furnace and fluorescent lights in that room generate a lot of noise on that circuit.
     
  11. kelbro

    kelbro Member

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    What is the temperature where the scale is located?

    How long are you letting it warm up before you calibrate it?

    Are there any drafts in the area?

    Fluorescent lights nearby?
     
  12. ny32182

    ny32182 Member

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    73.6 degrees F.

    Not letting it warm up for any significant time before calibrating for the first time.

    No drafts in the area. I have been careful about that.

    No flourecent lights nearby.


    ...I did not know that noise on the line would affect it. I do not have a battery with me, but I will get one and try it out when I get a chance.

    I am not loading up to max load here, so if it is only off by .1 or .2, I think I am safe to continue this loading session. I just won't recalibrate, and will check with several weights throughout.
     
  13. moosehunt

    moosehunt Member

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    Some confusion here between accuracy and precision. As a reloader, one doesn't need a high degree of accuracy. You do want a high level of precision. Accuracy refers to being correct. Example: If a specific bullet weighs a known 70.0000 grains, and on your balance (it's not a scale--a scale is for linear measurement) measures the weight of that bullet at 70.2 grains, it's accuracy is off by .2 grains (at that weight). Weighing your powder within an accuracy range of even a grain is not important. Don't go ballistic now--read on. What is important is precision, which is repeatability. Example: If we take that same bullet and weigh it 5 times and it always reads 70.2 grains, you have precision. If it weighs 70.3, then 70.1, then 70.4, then 70.2, then 70.1, you don't have good precision. It doesn't really matter if you know exactly what your powder charge weighs, i.e. accuracy (within limits), but it is important that the weight reading is always the same, i.e. precision. You want the same charge each time (precision), but the fact that a different balance might give a different weight reading for that charge (accuracy) doesn't matter. It won't effect you (your loads). Poor precision will effect your loads.
    So, don't worry about chasing accuracy, especially since, unless they are very expensive, your check weights doubtfully are very accurate themselves, and certainly using a bullet as a check weight does not provide an accurate measurement. Evaluate the precision of your balance by measuring the reading of a single object several times over. To really evaluate precision, you need to do this at several different weights. It is common for a balance to be accurate in a relatively small range, but precise over a much larger range. Hope this helps.
     
  14. JackOfAllTradesMasterAtNone

    JackOfAllTradesMasterAtNone Member

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    According to the manual for that scale:

    SPECIFICATION:
    750.0 GN / 0.1 GN
    50.00 g / 0.01 g

    I would say that there is an issue, according to what you've posted here. But, your error is what, Nine Tenths of one percent? My RCBS 10-10 balance beam scale isn't near that accurate, and my rifles still shoot minute of angle. Don't count on bulk packed match bullets being any better than +-1% in weight. Sierra's are quite acceptable at +-2%. And if you're not using benchrest/competition dies, then I don't think that three one hundredths of a grain is going to matter.

    Still, you did pay for that accuracy, so I would call RCBS about it. They have great customer service.

    Yes, variables with electricity voltages or frequency can affect the performance of an electronic scale. Humidiy and temperature too.

    -Steve
     
  15. jacobhh

    jacobhh Member

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    I agree with the last two posts and as you wrote
    your depending on your check weights for accuracy.
    The scale spec. is probably for linearity and repeatability
    with percent of reading and range caveats thrown in.

    The reality is for $100 you probably bought a scale
    adequate for your application and you might go
    through half they're inventory to find a better one.

    I don't know who manufactures the 750, maybe Ohaus
    but if you really want lab precision in that range check out
    http://balances.com/acculab/vicon+scale.html


    If you really need better precision
     
  16. redneck2

    redneck2 Member

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    You're talking .01 grams. I'm too lazy at this point to convert to grains, but I'm thinking this is pretty small. Guys get all torqued up over .1 grain. Trickle .1 grain of powder and see how much it really is. Almost invisible. Also, you're 23.5 grain might actually be 23.54. Next time it mis-reads by .02 and is thinking it's 23.56 so it rounds up instead of down.

    Moving a bullet around in the pan, partucularly on a balance beam can change the reading.
     
  17. kelbro

    kelbro Member

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    Let it warm up for 30 mins or so and repeat your test.

    Plug into one of the good plug strips with surge protection.

    Your accuracy should improve.
     
  18. Ridgerunner665

    Ridgerunner665 Member

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    moosehunt has a valid point.
     
  19. ny32182

    ny32182 Member

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    Thanks for the input guys, you're probably right. From now on, I'll let it warm up a little, then calibrate, and if the check weights come up the same or very close, I'm probably good to go.
     
  20. jak67429

    jak67429 Member

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    you might also want to make sure that the scale is level. I had problems with the dillon determinator and called them they said to use batteries only make sure of no draft and make sure it was level. after i leveled the scale my problems went away.
     
  21. ny32182

    ny32182 Member

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    That sounds like a good idea; I will try to check that.
     
  22. The Bushmaster

    The Bushmaster Member

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    I have a RCBS (Pact) Powder Pro electronic scale and a RCBS 5-0-5 balance. Both read the same within +/-.1 of a grain of each other. I believe that is within specification. My Powder Pro came with a 20 gram and a 50 gram check weights. After calibrating the Powder pro and re-weighing the check weights they are 19.9 and 49.9 respectively. Never been of any real concern to me...

    My RCBS Powder Pro will repeat every time +/- .1 gain and it's 18 years old. You do have to give it a 15 minute warmup though...

    By The Way...I have one 4 tube florecent over head light in a small room (10' by 8') that is the Gun and Reloading room and it does not seem to have any effect on the Powder Pro...The RCBS Powder Pro has no batteries at all. It has an adapter that plugs in to house current...
     
  23. Walkalong

    Walkalong Moderator

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    Electronic scales are finicky little boogers. I lost patience with mine and it went away.

    I had a RCBS 505 for years and it worked great. It got knocked off the bench and broken recently. I replaced it with a Redding. Not because I did not have great luck with the RCBS, I did, I just wanted to try the Redding. It is as good as the 505, well, so far. It will have to do great for a few more years to match up. I actually prefered the way the 505 was set. I kind of wish I had antied up for the RCBS 10-10.
     
  24. xsquidgator

    xsquidgator Member

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    I have the same scale (RCBS 750) and have noticed that it is sensitive to temperature changes. When I open my garage door and it's cold out, within 20 minutes the zero on the scale can drift by up to 0.5 grains. I suspect also that the scale, although solid state, needs time to "warm up". I've frequently seen zero change by up to 0.5 grains over the first half hour it's turned on, at times when I don't think temperature was a concern.

    I've never weighed my calibration weights like you have, I'll have to check that out. I did compare my RCBS 750 when I first got it against my Lee 100 grain balance scale, and it did pretty well within the 0.1-0.2 or so grains precision I could measure with my lee scale. I leave my 750 plugged in and turned on most of the time to avoid these problems, and I recalibrate it with the 20 and 30 weights when I think it's off. I keep an empty 9mm casing (60.8 to 60.9 grains) and a 125 grain plated bullet with the scale to act as my own check weights. I don't know what they ACTUALLY weigh, but they still make good constancy checks.

    By the way, I love my RCBS 750. My first electronic scale was one of those $30 battery-powered 750 grain scales that all the big box stores sell with their logo on it, at best it was sort of ok. Mine broke after 6 months and I finally came to my senses and bought the RCBS ($80 to $120 IIRC) - oh it is 10x better than the cheapie battery powered scale I used to have.
     
  25. USSR

    USSR Member

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    +1. And I am a finicky little booger when it comes to reloading, therefor, I reload strictly with a quality balance beam scale.

    Don
     
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