I don't think my scale is accurate


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ny32182
February 21, 2008, 08:57 PM
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...

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ny32182
February 21, 2008, 09:11 PM
Furthermore, according to the chart here:

http://www.metric-conversions.org/cgi-bin/util/conversion-chart.cgi?type=5&from=3&to=17

I am supposed to be getting 308.6 and 463.0 grains for the 20 and 30 gram check weights, respectively. On this current calibration, I am getting 309.1 and 463.6.

moosehunt
February 21, 2008, 09:16 PM
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.

ny32182
February 21, 2008, 09:21 PM
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?

ny32182
February 21, 2008, 09:38 PM
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.

Crimp
February 21, 2008, 09:53 PM
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?

ny32182
February 21, 2008, 09:57 PM
Unfortunately, no.

Ridgerunner665
February 21, 2008, 10:00 PM
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.

DJW
February 21, 2008, 10:02 PM
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

Idano
February 21, 2008, 10:02 PM
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.

kelbro
February 21, 2008, 10:34 PM
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?

ny32182
February 21, 2008, 10:45 PM
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.

moosehunt
February 22, 2008, 03:03 AM
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.

JackOfAllTradesMasterAtNone
February 22, 2008, 03:08 AM
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

jacobhh
February 22, 2008, 06:40 AM
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

redneck2
February 22, 2008, 07:50 AM
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?
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.

kelbro
February 22, 2008, 08:57 AM
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.

Ridgerunner665
February 22, 2008, 09:07 AM
moosehunt has a valid point.

ny32182
February 22, 2008, 09:45 AM
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.

jak67429
February 22, 2008, 10:02 AM
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.

ny32182
February 22, 2008, 10:17 AM
That sounds like a good idea; I will try to check that.

The Bushmaster
February 22, 2008, 10:35 AM
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...

Walkalong
February 22, 2008, 10:44 AM
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.

xsquidgator
February 22, 2008, 10:52 AM
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.

USSR
February 22, 2008, 11:05 AM
Electronic scales are finicky little boogers.

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

Don

rcmodel
February 22, 2008, 02:13 PM
The load-cell on any electronic scale is very temperature sensitive.

I either plug mine in the night before (or just leave it plugged in & running) and calibrate it when I get ready to use it the next day.

If I don't, it drifts off calibration during a reloading session.

I also found that removing the post that bears on the load cell & blowing it out with a can of keyboard duster occasionally helps repeatability.

rcmodel

moosehunt
February 22, 2008, 03:00 PM
The comments a lot of you have made here have created a question from me to you users of electronic balances. I have never used anything but a beam balance for loading (RCBS purchased in the mid '60s--it's green, but says "manufactured by Ohaus" right on it), but have been considering an electronic with the associated powder measure. I weigh every stick powder rifle load I make, and as is obvious from my previous comments here, precision (repeatability, remember?) is what I want. Am I likely to get it from these electronics? Or would I be dissatisfied, reverting back to my beam balance and cussing the waste of my money.

ForneyRider
February 22, 2008, 04:00 PM
I've been shopping scales, manual and electronic, haven't seen any that offer more than 1/10 grain accuracy.

RCBS digital scale has cover to keep wind from affecting the measure.

CBP
February 22, 2008, 05:15 PM
A set of check weights, calibrated in grains, not grams, is the best way to check the accuracy and precision of your scale. Keep an eye on Ebay or pick up a set on-line or locally. $20 - $35 is the going price.
Most sets will have weights of 0.5 gr, 1 gr, (2) 2 gr, 5 gr, and higher grains. This allows you to pick a nice range of combinations. For example, if you want to load 4.3 grains of powder, select the combination of weights that will give you 4.5 grains. Zero your scale first, put the weights in the pan,set your scale to 4.5 grains, and place on the scale. As stated in an earlier post, if your scale settles on zero (or correct weight for electronic) than your scale is accurate. Take the pan off and place it back on several times to make sure you get the same reading. This checks the precision. Since you picked the weight combination that is closest to your desired charge, you can be confident that your scale will be correct.
I use an RCBS 5-10 that is fairly new to me and a Franford Arsenal Digital. The RCBS is precise and accurate to the 0.1 grain. The digital is good to +-0.1 grain, mostly. I use the digital when setting up the micro-charge bar or Auto Disk just to get the approximate weight. Then I'll set the RCBS to the desired weight and use it to check the powder loads.
I would advise using the check weights whenever you have to make large adjustments to the scale, such as moving the 10 grain poise. There is always potentionial for a slight shift in the poise which can affect its accuracy.
I reload handgun calibers, so I've checked my scale out in the 3 - 8 grain range. I purchased a Cabela's set off Ebay which has a total weight of 1500 grains. It's way more than I need, but it's a nice set since ALL the weights are marked. From what I read on of reviews on Midway, the lighter RCBS and Lyman weights are not marked. Hopefully it should last me a lifetime. It does give me confidence that my powder charges are correct. Even using two scales, I was getting slightly different readings, so now I know which one to trust.

Steve C
February 22, 2008, 05:32 PM
You can spend too much time searching for perfection in measurement that matters little in the final performance of the product, in this case the ammunition. + or - a 1/10 grain is completely adequate in handloading.

A 1/10 grain is about 1 or 2 flakes of powder depending upon the powder. A more precise scale does nothing for you.

The very small variation in target impact due to bullet drop explained by the small variation in powder charge is insignificant when compared to the effects of wind and shooter error.

moosehunt
February 22, 2008, 07:54 PM
Steve C, I don't believe anybody with any knowledge at all would disagree with you regarding +/- 0.1 grain. Maybeso, in fact probably so at 0.2 grain, but even then, not a whole lot. And if a guy is loading that close to a preasure wreck, he's way to high anyway.

xsquidgator
February 23, 2008, 10:20 AM
I've been shopping scales, manual and electronic, haven't seen any that offer more than 1/10 grain accuracy.

One thing about the digitals that I hadn't realized - I think they all say +/- 0.1 grain, but that's not exactly true for all of them. My RCBS 750 *is* 0.1 grain precise, that is it reads out to nearest 0.1 grains. <It's accurate to this much also, at least, it agrees with my beam balance scale so I trust it>

The cheaper ~$30-$40 750 grain scales aren't necessarily. The one I had, a generic one that stores like Cabelas and GM put their logo on but all come from the same chinese factory, read out in increments of 0.2 grains. It's still probably accurate to within a 1/10 grain but it's a pain in the neck. Mine would read out for instance 0.0, 0.2, 0.4, etc, so if I wanted say 4.5 grains I'd trickle up to 4.4 and then try to get the display to flip back and forth between 4.4 and 4.6 It's doable but a PIA.

If you want a digital, I'd spend $100 or more and get some sort of RCBS or another well-established brand. People kept telling me to not go cheap on my equipment but I didn't listen when it came to my scales. Now I know why they were telling me that.

brickeyee
February 23, 2008, 12:26 PM
The RCBS check set runs about $50.
You do not need lab type check weights.
These get a little pricey since they have to hit a specified value.
What you need is KNOWN value weights.

I actually have a set I made up years ago and weighed on an analytical balance.
The card inside the storage case shows the actual weight of each piece.

The biggest issue is making sure NOTHING CHANGES the weight.
No corrosion, no dirt, etc.

snuffy
February 23, 2008, 01:11 PM
First off, the OP is talking about this digital scale;
http://www.midwayusa.com/eproductpage.exe/showproduct?saleitemid=814722&t=11082005

The calibration weights are NOT check weights. They simply calibrate the scale. Check weights are precision made to weigh just what they're supposed to weigh. Here's the Lyman check weights.
http://www.midwayusa.com/eproductpage.exe/showproduct?saleitemid=612694&t=11082005

With this set you can go from .05 grains to all combined to 210.5. Without a set of check weights, you're simply guessing. Using a bullet means nothing as they can be a grain off and still pass inspection.

Those RCBS scales are made by pact. My RCBS powder pro bought in '96 pairs up with the pact dispenser bought is 2004 perfectly. Oh and it still works just great!

brickeyee
February 23, 2008, 01:25 PM
And even after using the cal weights, testing again with those AND a set of additional weights is a good idea.

Check weight DO NOT have to be any exact value, just a KNOWN value.

Load cell scales have temperature issues.
The actual change in resistance with weight is often LESS than the change in resistance with temperature.
They need to warm up and be used in a stable temperature environment.
ANY time varying magnetic field the scale is exposed to can introduce noise into the measuring circuit.
The actual measurement circuit is normally done with an AC signal to prevent DC variations in the circuit from causing problems, but a changing magnetic field will couple into the load cell.

It is possible to create load cells that are pretty immune to magnetic effects, bet they start getting expensive.

The temperature effects can also be canceled out, but that gets expensive also.

Most of these techniques use a second load cell to cancel out the changes in the one taking the measurement. If the two cells are identical and in the same environment they you can use the second cell to cancel the changes in the actual one making the measurement.
It becomes a rather expensive exercise very quickly.

I normally just leave my digital scale plugged in all the time, then calibrate it before each use.
Be sure to allow enough time for the scale to settle between changing the cal weights.

Better scales use 2 or 3 weights (or combinations of weights) to try and adjust for both absolute value and linearity.
The calibration method can be anything from 'best straight line fit' to more sophisticated algorithms that actually try top cancel out linearity errors.
These things are a bit if a PITA to design, since the processing of the load cell signal needs to be carefully filtered and smoothed or the numbers would never stop bobbling around.
Trickling powder onto them can be hit or miss.
If you go to slow the electronics may 'cancel' the change thinking it is just random wander in the load cell.

ny32182
February 23, 2008, 09:25 PM
Thanks for all the input guys...

This last time using the scale, I let it "warm up" for half an hour before calibrating it, and then it weighed my test bullet consistently at 68.4gr throughout the loading session. So I think a lack of warmup was probably responsible for what I was seeing.

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