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RCBS Chargemaster accuracy test

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Unread 05-02-2011, 12:00 PM
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Join Date: Jan 2005
Location: Searcy, Arkansas
Posts: 700
RCBS Chargemaster accuracy test

I have been using the Chargemaster for several years and have been (still am) happy with it. However I have questioned if the standard digital reloading scale resolution of 0.1 grains is accurate enough for truly precision loads. I finally bought a Sartorius M-Prove model lab type scale. (replaces the Acculab scale in the Sinclair catalog..... I think Acculab is no longer around, at least Sinclair and other distributors no longer carry it) The Sartorius has a resolution of .02 grains. I decided to do a quick test to compare the two.

The Test: Both scales are set up side by side on a solid bench further isolated with a 100 lb granit slab isolated from the bench by 1" of high density foam rubber, the scales each have 1/4" of foam between each "foot" and the granit slab. A conditioned and isolatated power source is used for each. Each scale is leveled and calibrated.

I chose two different powders, H50-BMG which is a very coarse powder and US869 which is a very fine ball type powder. I chose these to represent the opposite ends of the spectrum of powder types. A charge weight of 100.0 grains was chosen with 10 samples of each powder type.


RCBS Chargemaster Sartorius M-Prove
1. 100.0---------------- 99.90
2. 100.0---------------- 100.18
3. 100.0---------------- 99.98
4. 100.0---------------- 100.08
5. 100.0---------------- 100.04
6. 100.0---------------- 100.04
7. 100.0---------------- 100.28
8. 100.0---------------- 99.98
9. 100.0---------------- 100.18
10. 100.0--------------- 99.98

Average charge 100.06 gr.
ES (largest spread between any two charges) .38 gr.
40% of charges are equal to or more than .1 gr. from desired weight.


1. 100.0-------------------- 100.14
2. 100.0-------------------- 100.12
3. 100.0-------------------- 100.02
4. 100.0-------------------- 100.06
5. 100.0-------------------- 100.04
6. 100.0-------------------- 100.10
7. 100.0-------------------- 100.06
8. 100.0-------------------- 99.96
9. 100.0-------------------- 100.12
10. 100.0------------------- 100.10

Average charge 100.072 gr.
ES .18 gr
50% of charges are equal or more than .1 gr from desired weight.

My thoughts: This was a fairly small sample, but results indicate a significant variation in the charge weights. To me, the ES number is the most important. Even with the large (over 100 gr) powder charges I use a difference of .38 gr or even the low of .18 gr for US869 will make quite a difference in muzzle velocity.

My intention when I bought the Sartorius scale was to continue to use my Chargemaster, but set it for a light charge then weigh on the Sartorius scale and trickle up to the exact charge.
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Unread 05-02-2011, 01:28 PM
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Join Date: Mar 2008
Posts: 602
Re: RCBS Chargemaster accuracy test

Probably a dumb question but is this the charge that was thrown com the charge master with no corrections. For example if I am going for 100 grains out of 10 mine might throw 5 or 6 at 100 and the other 4 might be off by. 3 or so. It will tell me if its over or under then i correct it. What my question is: in your results is your documented wieghts after you corrected it to show 100 grains or is just why ever it originally threw? This is great informtion- thanks for posting
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Unread 05-02-2011, 02:32 PM
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Join Date: Jan 2005
Location: Searcy, Arkansas
Posts: 700
Re: RCBS Chargemaster accuracy test

lamiglas, Not a dumb question at all. For the sake of keeping the initial write up from being too lengthy I did not include all the details of the test.

During the test, the Chargemaster went "over" on 2 charges, those were simply dumped back into the hopper and re-dispensed. 6 charges were "under" and I trickled powder in until the display was stable at 100.0 grains. From past experience, my Chargemaster tends to dispense about 30% to 40% of the charges "light" by .1 to .2 grains. Often it will stop on the exact charge then after it sits for a few seconds will "drop" by .1 or .2. It is actually fairly rare for me to get "over" charges. Each charge weighed was allowed to sit on the scale(s) for 1 min to ensure the reading was stable.
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Unread 05-02-2011, 02:46 PM
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Join Date: Mar 2008
Posts: 602
Re: RCBS Chargemaster accuracy test

Based on other information you provided I figured that is how you did it but just wanted to confirm.. I have been using this to load for my 338 edge and I have 647 rounds down tube in the last year. Shots varying from 600 yards to a mile. Mostly 1000 yards plus. I have been very happy with the load and how they shoot but I am very interested to see the responses you get. I always check the first load against my old rcbs scale but it's not any more accurate so I would never know if im off by the amount that you are seeing.
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Unread 05-02-2011, 08:07 PM
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Join Date: Mar 2009
Location: Colorado
Posts: 8
Re: RCBS Chargemaster accuracy test

RDM - I too questioned the accuracy of my RCB's and Hornady electronic powder throwers; thus, I purchased the exact same scale from Sinclair.

First and foremost I find your hypothesis on the RCBS Chargemaster to be accurate; additionally, I found the Hornady Lock-n-Load Autocharger to be no worse and no better with respects to accuracy.

I now simply have my powder thrown .1 grain short & trickle up on the Sartorius M-Prove. This has DRASTICALLY cut down my standard deviation on my .223 reloads.
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Unread 05-02-2011, 08:08 PM
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Join Date: Aug 2003
Location: NC, oceanfront
Posts: 4,189
Re: RCBS Chargemaster accuracy test

It's hard to tell from this if either scale was best used..
Efforts aside, you can't just set-n-forget a dynamic load with accuracy. Which is why relaoding scales are better -for reloading,, than lab scales.

I'm confident that with a little tinkering/tuning, you'll get a lot better with your CM.
For one, you'll find that you need to disturb the pan, allowing better readings to re-settle.
You might also notice that the CM can be and should be tuned to each powder specifically.
There is timing, and a sense for each charge quality as observed.

The route you've chosen(validation with higher resolution) will really pay off by helping you operate the CM better.
It's exactly what I did, with the same scale(well, acculab), and I got good enough with the CM (tinkered & tuned) to discontinue validation. I now know my charges are right, or wrong, with better accuracy than the CM scale is rated.

This is similar to issues people create with QuickLoad reloading software. Some expect professional results, with novice use, and that don't EVER happen by chance.
You must make it happen.
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Unread 05-02-2011, 08:46 PM
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Join Date: Jan 2005
Location: Searcy, Arkansas
Posts: 700
Re: RCBS Chargemaster accuracy test

I agree, I suspect I am at the begining stage of yet another learning curve.
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