Digital Scale - Am I Expecting Too Much?

[blacklisted]

I have been using an RCBS Rangemaster 750 digital scale, and have encountered a potential problem. I do tend to over analyze things occasionally, but I can't let this one go.

This scale is advertised as measuring to +/- 1/10 grain. Obviously, that means that the measured values should be in a .3 grain range.

The problem is that I have to re-zero the scale during use, because the empty weight of the pan will occasionally vary by +/- .3 grains (it's usually .1). I don't know if it is due to static electricity or magnetic fields from the fluorescent lighting, but the end result is me having less confidence in the scale.

I'm trying to get a feel for my powder measure, so I decided to throw a bunch of charges and write them down. I found a setting that would be around 27.5 grains of Varget, so I started.

27.4
27.4
27.5
27.5
27.5
27.5
27.4
27.5
27.4
27.5
27.4
27.5
27.5
27.5
27.4
27.5
27.5

At this point I was thinking, "Wow, it's going great."

So I continued.

27.6
27.5
27.6
27.5

A few minor deviations are to be expected, so I continued.


27.2
27.2
27.3
27.3
27.4
27.5
27.6
27.8

What the hell?

Because this is a powder measure not really known for metering Varget perfectly (RCBS Uniflow, competition model), +/- .3 grains is not really a problem and would surely be safe if the charge was safely under the maximum (I would be comfortable with .5 grains under maximum).

However, I knew from my previous tests of this scale that it could be and probably is giving me an incorrect value.

I carefully poured out the 27.8 grain charge and placed the empty pan on the scale. There was a .2 grain difference from zero. I re-zeroed the scale, and poured the charge back in to the pan. 27.6 grains.

I continued.

27.4
27.6
27.6
27.3
27.4
27.5
27.7
27.4
27.7
27.5
27.7
27.5
27.3
27.7
27.5

The sudden appearance of 27.7s was a minor disappointment, but not unexpected. Some of these flickered between 27.6 and 27.7, so they were probably in the 27.69 to 27.71 range.

The average charge weight was 27.5 grains, high value 27.7, and low 27.2.

At this point, I'm confident in the powder measure (more confident than I am with the scale). This data string confirms the positive results I have had in my other experiments.

The issue is that this scale can cause problems when weighing charges individually. If I throw charges slightly under what I want and trickle powder to bring the value up, I can't be sure of the true weight of the powder charge. I do notice when there is a problem, because I check to make sure it is zeroed when I put the empty pan back on the scale. I don't know how much of an effect these variations will have on velocity and accuracy, but I guess I'll find out when the weather improves and I chrono my test loads (all charges weighed individually).

Would my best option be to buy a balance beam scale, or shoud I just replace the digital scale?

[halifax]

I, too, am not impressed with these plastic digital scales. The first one I bought was an RCBS Micro-Pro. It has a built-in "feature" that does an auto-zero if the pan is empty and varies from zero by +/- 0.2 grains. That one screwed me up for a while. Then the plastic platen began to swell and lose it's plastic sheen as will happen with all plastics. After that it didn't freely move up and down in it's load cell guide and reading became unreliable. Stopped using it after that for powder but still use it for cases and bullets.

I work at a lab so I know what quality balances are like. First they don't have plastic parts in the load cell movement or platen. Case yes, but if it moves it's metal. Some of our benchtop balances have been working for 15+ years. Same technology as the Micro Pro but without the cheap plastic. BTW, the lab grade balances don't have (or need) the auto-zero feature. If the human operator feels the need to zero it he does so manually.

Despite this, I bought an RCBS Charge Master 1500. I fully expect that some day the plastic platen and load cell guide will degade and begin to bind. It's still cheaper than a laboratory grade balance though.

As for your issue, I'd guess it's either that damn auto-zero feature or the platen has started to bind in the guide.

Do like I do and verify weights using a beam balance.

[PistolPete75]

extruded powders like varget, imr 4064, imr 4895, rl15, etc are difficult to measure. all electronic powder measures are like this.

[NRAhighpowershooter]

I have had my Dillon electronic scale for over 8 yrs now and I don;t have any measuring problems like what the OP has stated.......

[blacklisted]

This isn't an electronic powder measure. I didn't mean to blur the distinction between my scale and powder measure so much.

extruded powders like varget, imr 4064, imr 4895, rl15, etc are difficult to measure. all electronic powder measures are like this.

[blacklisted]

I have had my Dillon electronic scale for over 8 yrs now and I don;t have any measuring problems like what the OP has stated.......

I have been looking at the Dillon D-terminator, which I would have bought instead of this one had I known about it before. It's only 40 dollars more, and I like the design.

[50BMGBOB]

I find that electric scales are vary voltage sensitive. Battery voltage can vary as they run down and line voltage (AC adapter) can vary as well. I use a UPS (like for your computer) with a built in line filter. Don't have anything else plug into it while you use the scale. And I leave my scale on all the time so the electric parts of the scale warm up and maintian a constant temp. This will help with any scale. My next scale will be a DI as they have the best, most stable readings. The lower end models are actually reasonable for a reloader to buy, at least they aren't much more $$ than I paid for the Dillon scale that I have now.

[f4tweet]

I am looking into an electronic scale. I was told you had turn them on and let them warm up and stabilize for at least a 1/2 hour before use. If this scale is not stable, should I just stick with my 10-10?

[Kiba]

I have an older style Dillon D-Terminator I bought from a friend.

Works great. It does take about 15 minutes to warm up and stabilize, and then I use a set of check weights to verify the scale in the powder charge range I plan on verifying.

The only issue with it is using a trickler on it; once the arrow on the display has turned on indicating the reading is stable, if you very slowly trickle powder in the scale will not register the additional powder and you can overcharge by as much as you want and it will still show the first mass that it stabilized on. When you remove the pan to dump the powder then place the pan back on the pad it will not return to zero... indicating you have just overcharged that load. The first couple loads I made using the D-Terminator had a very large extreme spread and my misuse of the scale was the problem. After some experimenting I found that you have to trickle in additional powder before the stabilization "arrow" is on the display, and once the arrow turns on it's best to disturb the scale (I just lightly tap it) to knock it off stable and then start trickling in more.

Whenever I check my Dillon with the check weights after the warm-up period it is always right on the money. Any powder variations I attribute to the powder and/or throw, because the check weights are always correct. I'd suggest investing in a check weight set, RCBS has a good one for about $25. I verified the RCBS set on one of our $7000 Sartorius lab analytical balances at work. They were not perfect but well within the precision needed for checking a powder scale.

The variations you are seeing in your throws seem about right... I was making some Varget loads tonight for .308 around 44 grains and my Redding #3BR measure was varying around .2 grains. Varget certainly meters far better than say "Lincoln Log" 4064, but it's nowhere near as good as most of the Vihtavuori powders which are usually excellent when it comes to metering.

However, getting different weights for the same charge when you repeat the measurement is odd... which is why I would suggesting picking up a set of check weights.

[Ahhnother8]

Try a Denver Instruments MXX-123. It is accurate to 1/50th of a grain and retails for about $300. One kernel of Varget weighs .02 grains, and the scale will recognize it. Once you experience this level of accuracy, you will never go back!

In the .308, I load 47 1/2 grains of Varget for a 155 bullet. With the BR30 powder meter, most come out within a tenth of a grain or so, but some will be a half a grain high OR low. Very few are within the 47.48 to 47.52 window that I am looking for, so just trickle in. For anything under 800 yards, 47.46 to 47.54 is acceptable. It just doesn't seem to matter that much at shorter ranges. YMMV

Lane

[TonyM]

I've been using a PACT Digital Precision model for a few years and don't have any issues. I calibrate it with the included weights about once a month or so. As long as the bench it's on is stable, so are the readings.

[Waldog]

50BMGBOB is right on when he states that electronic scales are voltage sensitive. You would be amazed how much the voltage fluctuates on a household 115 vac circuit. To get optimum performance from your electronic scale with very little wt. variation, do these TWO things:

1. Make sure your scale is plugged into a "clean" outlet that is not shared with any other "cycling loads", like a refrigerator or freezer, washer/dryer, air compressor, etc. ANYTHING that cycles.
2. Plug a "regulated" surge surpressor into the "clean" outlet and then plug your electronic scale into the surge surpressor.

By doing this you will signficantly cut down on voltage fluctuations and think you are using a $500 Lab quality scale.

Try i! It works!!

[maxicon]

You can test if the scale is accurate in the scenario you mentioned pretty easily.

Find something easy to handle that won't absorb moisture or skin oil (like a screw, piece of wire, whatever) that weighs about the same as your charge.

Weigh it 100x in a row. Come back in an hour and do it again. Do it at different times of the day and night. If the scale is unreliable, you'll find out soon enough (as well as how many measurements it takes to be sure there's a problem), and you can start testing for what's making it so, like the circuit it's on, air currents, etc.

[CSACANNONEER]

I find that electric scales are vary voltage sensitive. Battery voltage can vary as they run down and line voltage (AC adapter) can vary as well. I use a UPS (like for your computer) with a built in line filter. Don't have anything else plug into it while you use the scale. And I leave my scale on all the time so the electric parts of the scale warm up and maintian a constant temp. This will help with any scale. My next scale will be a DI as they have the best, most stable readings. The lower end models are actually reasonable for a reloader to buy, at least they aren't much more $$ than I paid for the Dillon scale that I have now.

+1 on everything Bob said!