Calibrating powder dispensers

[bdbrown66]

Here's a question for all you smart guys and experienced reloaders:

I have an RCBS Chargemaster. According to the instructions, you're supposed to calibrate it each time before use. But if the scale accurately registers the correct values for the known check weights, what is the point of calibrating? Isn't the whole point of calibration to adjust the scale so that it is consistent with a known weight? I just don't understand the point of doing the calibration, if the scale is already reporting the correct weight.

Tell me what I'm missing here.

 

[flyingagg]

You do it because your safety depends on it. You want to make sure it is calibrated. My 20 year old PACT has never needed calibration, but every time I use it I go through the process. It does not take much powder to end up with an unsafe load.

 

[hunter24605]

My guess would be that in this litigious society, its an abundance of caution. Some may not take the time to verify with the check-weights and just assume it's dispensing accurately. Calibrating before each use reduces the risk. Again, just my guess

 

[bdbrown66]

Oh, I do verify it against the check weight. But my question is, what is served by going thru the calibration process, if it weighs the check weight correctly? What is being "calibrated," at that point?

 

[BruceP]

I’ve had the same thoughts but then the calibration process really doesn’t take long so I do it each time.

Bruce

 

[BruceP]

I’ve had the same thoughts but then the calibration process really doesn’t take long so I do it each time.

Bruce

 

[Nimrod84]

Sorry for the long response.

The short version as I understand it is that the Chargemaster 1500 has a self (dynamic) calibrating feature and that over time it can go off the rails, causing errors to stack up on itself until a hard user induced calibration is used. A good video of that is at https://www.youtube.com/watch?v=JmxBSOOL7Ks. Additionally the scale of the Chargemaster 1500 is supposedly accurate to someplace in the hundredths place (0.0x), so while a check weight might show the correct weight, the rounding of other items to the nearest tenth (0.1) might be skewed.

The long winded explanation from my experiences is that I calibrate my Chargemaster 1500 at the start of every loading session as it gives me peace of mind that it is setup correctly. Usually after 10-15 loads I need to tare the scale as mine drifts - as in the above video. If I don't calibrate before use it almost always drifts within the first couple of loads and then it might wander by 0.4+ grains which requires me to re-calibrate. By calibrating at the start, I know I should be within an acceptable range by just taring the scale as needed.

I have a Gempro 250 that I confirm my Chargemaster 1500 weights on. I do not calibrate my Gempro 250, as it stays pretty solid for me. I do not trickle on it or otherwise add weight on the scale as it will otherwise wander as it isn't designed for dynamic loading - as noted at the end of https://preciseshooter.com/blog/ScaleRe ... ro250.aspx.

The Gempro and a Layman M5 have shown that even with periodic taring of a Chargemaster (that wasn't recently calibrated), the Chargemaster's dispensed and displayed weights even if they match each other aren't always correct - i.e. a dispensed weight might be set for 54.5 grains and the chargemaster might show 54.5 grains, but the Gempro and a Layman M5 might show 55 grains. This is on top of having the 50 gram check weight show 50 grams. With calibrating the Chargemaster 1500 at the start, it will almost always be within 0.1 grains of the Gempro and M5 through the initial 10-15 loads and then for another 10-15 loads after it is re-tared.

 

[bdbrown66]

Nimrod,

Interesting, thank you for taking the time to post all of that. I will take a look at the video you linked. And now, I'm going to have to test my Chargemaster to see if it drifts like yours. Does it seem to matter how large the dispensed charges are?

Brian

 

[DrMike]

I suppose it is the years spent in the lab, but I calibrate all electronic gear. Habit, but a good one, I believe. Electronics can deceive you, so better to be cautious.

 

[diverdown]

Doc, If I remember correctly you have to be watchful of Fluorescent lighting. The minimum distance is supposed to be 6 feet from any electronics if I'm correct.

 

[DrMike]

There are a number of factors that can work against electronics. Again, it is to a great extent a matter of being conscious of unexpected results. When such does occur, make certain you've ruled out that which is most likely. Calibrating your scale eliminates what is arguably the most probable cause of aberrant results.

 

[Nimrod84]

"Does it seem to matter how large the dispensed charges are?"

I don't see that charge weight matters much for me - I'm mostly in the 46-60 grain range.

I leave the Chargemaster and Gempro on for months - only time I turn them off is when I have a power outage or am going to be gone for an extended period of time.

Temperature (below 64-65 degrees it goes wonky) and temperature swings, weight left on the pan, poor leveling and static have been the main causes for my wandering zero. I have never used Fluorescent lighting in my home and have been pretty cautious with LED as the cheaper bulbs / lighting units can cycle like Fluorescent. I tried an LED light in the same outlet as the Gempro 250 and the Gempro went crazy and wouldn't hold zero...

Historically I've had as bad as 0.5-0.6 grain discrepancies on the Chargemaster, I could see a 0.3 grain change just by putting my hand by the plastic platen.

With a number of fixes, Area 419 platen and pan, granite surface plate, nozzle reducer, M1 class calibration / check weights and a UPS (power regulator) I'm getting the results I mentioned in my first post. The Chargemaster is going great and will often maintain a 0.02 + or - difference from the target weight and Gempro verification - on a bad day it maintain an average + or - 0.06 spread with an es in the + or - 0.16 range. With the weak link possibly being the Gempro; which I consider to be accurate to 0.06 + or - grains as on a bad day it can be sensitive to wind or thermal changes, good days the Gempro is + or - 0.02.

Last night I reloaded 29 rounds, the first nine rounds were IMR 4451 at 56 grains for a light 30-06 150 grain plinking load. After calibrating the scale the first 5 or 6 rounds where within 0.02 grains of my 56 grain target weight with two dead on. I then had one that came in at 54.92 grains on the Gempro and the Chargemaster said 56 and the rest of the rounds were well within + or - 0.4 grains.

For the next 20 rounds (I did not re-calibrate the scale), but I changed powder to RL-22 for a 280 AI workup using 150 grain Scirocco II's and did 1 round at 55 grains, doubles until 60 grains and 1 round at 60.5 grains. I had good agreement (+ or - 0.04 grains) until I hit 57 grains at which time the Chargemaster scale adopted a -0.1 resting weight which taring twice fixed right up after that agreement was holding within 0.06 grains mostly negative. At 60 grains (28th charge of the night) things went a little sideways, the Chargemaster indicated a 60 grain throw and the Gempro indicated a 59.88 grain throw. I believe the subsequent 60.5 grain throw came in at 60.46 grains.

 

[bdbrown66]

Nimrod,

I watched the video you listed above. At first it was concerning, but if you read the comments below the video, there is a good explanation of the cause. Basically, it's due to an auto-zero feature of the scale, designed to re-zero between throws. As one viewer pointed out, the RCBS literature states that the scale is supposed to measure +/- .1 grain, from 2-300 grains. So, unless you were seeing this behavior from your scale at or above 2.0 grains of charge weight, it was working as designed.

I intend to do some testing with mine this weekend. I still have my RCBS 505 beam scale, so I can only go to .1gr accuracy on it, but that will be close enough for my purposes. There will be a lot of things in my environment that will confirm or deny how my scale is behaving. For example, it will probably be 50 degrees or so out in the garage, and I have fluorescent lights.

Here's what I intend to do:

1. Turn on the unit, let it warm up for a few minutes, then verify zero using one of the check weights as I have been doing now.
2. Using a stick powder such as IMR 4064, throw 10 charges of 25.5gr, 10 charges of 35.5gr, and 10 charges of 45.5gr. These would represent (roughly) the loads that I would throw for .223, .243, and .30-06.
3. Confirm each of the throws in step 2 with the balance beam, and record the ones that are +/- of the target charge.
4. Calibrate the scale.
5. Repeat steps 2 and 3 and compare the results pre- and post-calibration.
6. Repeat steps 1 thru 5, using a fine ball powder (AA9), and charge weights of 7.5gr, 15.5gr, and 22.5gr. This will represent the types of charges I would use for my .40 S&W and .45 Colt.

It might take a while to do all of that, but it should provide some interesting results. I will report back on my findings.

Cheers,
Brian

 

[Nimrod84]

Brian,

Please let us know what you come up with.

Understood on the auto-zero function - is what I called "self (dynamic) calibrating".

My issue as noted during my last reloading is that my scale took a hard -0.1 grain weight with an empty pan which did not auto-correct to 0 when I got to 15 or 16 powder drops. If I hadn't tared the scale to correct the zero weight, the next charge weight would have normally bounced around. Additionally with my 2nd to last charge (28th of the night), the Chargemaster showed a 60 grain weight but the Gempro verified weight was 59.88 grains.

I can't track the exact cause of the two discrepancies / issues on my machine; but my guess is that my auto-zero doesn't zero on 0 but on something like + or -0.005 grains and that over 10-15 loads it ends up rounding up to a 0.1 grain difference from the initial zero point. The bouncing I see with a weighed charge I suspect is the scale trying to account for the initial rounding on the zero weight.

 

[BruceP]

I forgot to add that somewhere between every 5-10 charges I also check it on my RCBS 505.

Bruce

 

[bdbrown66]

OK, here is the followup, as promised. I apologize in advance for the long post, but I think the data is interesting.

To recap, I am comparing the thrown charges from my RCBS Chargemaster vs. the weight shown by my RCBS 505 beam scale. I threw 10 charges each with IMR 4064 (stick powder) in the following weights: 25.5gr, 35.5gr, and 45.5gr. I repeated these tests with only only using a check weight to verify the scale prior to beginning, and again after doing the whole calibration routine. I then repeated the entire process using Accurate #9 powder (which is very fine), in charge weights of 15.5gr and 22.5gr.

First, the data. The first column in each group is the weight shown by the beam scale prior to calibrating the Chargemaster, and the second column is after calibration. The last line in each group shows the average deviation from the Chargemaster's throw weight.

Powder: IMR 4064, 25.5gr Beam Scale Wt.
w/o Cal. w/ Cal.
25.4 25.4
25.4 25.4
25.4 25.4
25.4 25.3
25.3 25.3
25.3 25.3
25.3 25.3
25.3 25.3
25.3 25.3
25.3 25.3
Avg. Variance: -0.16 -0.17

Powder: IMR 4064, 35.5gr Beam Scale Wt.
w/o Cal. w/ Cal.
35.3 35.4
35.3 35.4
35.2 35.4
35.3 35.4
35.2 35.3
35.3 35.3
35.3 35.3
35.3 35.3
35.3 35.3
35.3 35.4
Avg. Variance: -0.22 -0.15

Powder: IMR 4064, 45.5gr Beam Scale Wt.
w/o Cal. w/ Cal.
45.5 45.4
45.3 45.4
45.2 45.4
45.3 45.4
45.3 45.4
45.4 45.4
45.4 45.4
45.4 45.4
45.4 45.4
45.4 45.4
Avg. Variance: -0.14 -0.1

Powder: Accurate #9, 15.5gr Beam Scale Wt.
w/o Cal. w/ Cal.
15.7 15.5
15.6 15.4
15.5 15.5
15.5 15.4
15.5 15.5
15.5 15.4
15.4 15.3
15.4 15.3
15.4 15.4
15.4 15.4
Avg. Variance: -0.01 -0.09

Powder: Accurate #9, 22.5gr Beam Scale Wt.
w/o Cal. w/ Cal.
22.4 22.5
22.5 22.4
22.5 22.4
22.5 22.5
22.5 22.4
22.5 22.4
22.5 22.4
22.5 22.3
22.4 22.4
22.4 22.4
Avg. Variance: -0.03 -0.09

My observation during this process is that the beam scale tended to weigh the charges about .1-.2 lighter than what the Chargemaster was supposedly dispensing. But, how to tell which one was more accurate. I dug out my little Frankford Arsenal digital scale and began to weigh charges on it, as well, just for another data point. Most often, it tended to agree with the Chargemaster, moreso than the beam scale. I could say, with reasonable degree of accuracy, that the Chargemaster was fairly consistent in what it was throwing, but no way of knowing if it was accurate or not. The beam scale seemed to think that it was throwing light.

The check weights that I have are what came with the CM and the FA scale, and they are 50 grams each, which is more than the capacity of the beam scale. After doing a little Google searching, I found a discussion where one fellow said that there is an almost-free "field-expedient" check weight available, courtesy of Uncle Sam. It seems that a new nickel, by regulation, must weigh 5.00 grams. While not precise enough to calibrate laboratory equipment, I thought that it would serve as a useful data point in my testing. So, after procuring a shiny new 2019 nickel, I placed it on each of the scales. Both the FA and CM weighed it at 5.00 grams, or 77.1 gr. (or 77.2 gr.). The 50-gram check weights come in at 771.6 gr., so it would be reasonable for nickel to be reported as either 77.1 or 77.2, depending on scale variations and rounding. But, close enough for my purposes.

Now, here's where it gets interesting: the beam scale weighed that same nickel at 77.0 gr. I tried it multiple times to see if there would be any variation, but it was pretty consistent. One time it came in at 76.9 gr. But if that nickel is a true 5.00 grams, then that would seem to indicate that my beam scale is in fact weighing things .1 - .2 gr. lighter than what they really are. That tracks with what the data in my experiment seems to show, as well.

Conclusions:

1. The Chargemaster seems to do what it's supposed to do, with the accuracy and repeatability stated in its specs.
2. Calibrating did not seem to make an appreciable difference one way or the other, over just using the check weight at startup.
3. Throwing finer powder is somewhat more accurate/consistent than throwing stick powder.
4. When working correctly, the Chargemaster is going to be as good as the beam scale + trickler for 99% of reloading scenarios...and much, much faster.
5. Quit worrying about it; go load, shoot, and enjoy.

Cheers,
Brian

 

[Nimrod84]

Thanks Brian, it will take a bit of time to really process your data. Your Accurate #9 variance seems to match up well with my variance. The IMR 4064 35.5 and 25.5 grain charges are a bit off from what I expect.

With the 35.5 grain charge you reported as low as 35.2 grains - which seems to be a little excessive. If it was throwing +0.3 grain charges that could be a bad thing.

I agree on the accuracy of the beam scales - my M5 goes in and out of calibration as the weight changes. It is pretty far off below 40 grains and then fairly good up until the mid 60 grains. Mine tends to read light as well - the knife edges / pivot points on mine need sharpening.

Main thing is that any scale is consistent with itself.

Thank you again for the data!

 

[bdbrown66]

"With the 35.5 grain charge you reported as low as 35.2 grains - which seems to be a little excessive. If it was throwing +0.3 grain charges that could be a bad thing."

Based on the data, I think the most likely scenario is that the beam scale was reading .2gr light, and the CM threw one at 35.4gr. Put those two together, and it looks like -.3gr.

 

[Nimrod84]

Brian,

I agree with you.

I had miss-typed the number. I meant the 45.5 grain as all the calibrated weights were 45.4 grains and you had an un-calibrated weight down at 45.2 grains with a bunch of 45.3 grains and one at 45.5.

I think that tells me that calibrating the chargemaster can be useful to do your beam scale reported all the calibrated weights at 45.4 grains, while un-calibrated varied by +0.1 or -0.2 from the beam scale weighing the calibrated charges.

However, I still need to digest the numbers a bit. Like the Accurate #9 at 15.5 grains which had charges at 15.6 and 15.7 grains. While the calibrated weights at 15.5 grains were all 15.5 or lower. The ES between calibrated and un-calibrated looks to be 0.4 grain, but what really gets my attention is that the un-calibrated gives higher readings than desired. I personally don't mind under charges, trickling is easy; over charges get my attention in a hurry.

Thank you again for the data and response.