I don't think my scale is accurate

[rcmodel]

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]

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]

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]

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]

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]

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]

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]

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]

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]

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]

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.