My Review of the RCBS ChargeMaster Lite Powder Dispenser.

[jimmykan]

That and the guy using it in 100˚ heat, I'm surprised the scale worked at all. My gem pro 500 refuses to work above 90˚ drifts very bad. But I agree. showing that the dispenser can hit a number don't mean a damn thing if that number is not correct. You have to verify it to a known standard.

I would disagree, in part, with that. While it is true that most of our consumer-grade scales and balances are not likely to be accurate, precision is what I really need in reloading. That is, the dispenser/scale needs to give us the same charge we specify, every time. For example, if we come up with a well performing round using what the scale tells us is 5.1 grains of Bullseye giving a 900 fps velocity time after time, then it is not important whether that charge is really 4.95 or 5.20 grains, only that it drops the exact same amount today as it did yesterday when we told it 5.1. Precision is more important to me.

One can acquire a set of check weights to get a better idea of how accurate your scale is, and whether it is giving you the same results every time.

Admittedly, I’ve been remiss in checking my new CM Lite after the first couple of uses, but I did check it with 100, 500 and 1000 mg weights. The scale didn’t register exactly the stated weights in each case, but it gave the very similar results two days in a row. Far superior to my ability to read a beam balance given crappy eyes, parallax, etc.

Doesn't have to hit the number dead on, and really, the variability can of course be non-zero.

What is key is to measure that target so as to understand the variability. The data as pulled from the CM 1500 is actually pretty impressive. And yet there are still people on this forum who do not trust it (just not good enough).

For those people, CM lite has no hope. But i want to know how that variability compares to the 1500. Same? I'll give it a shot. Worse? well, how much worse? if the CM 1500 is .75 grains variable on the sartorious (this is fake data, just an illustration), and the CM lite is 1.2 grains variable, well, I probably don't care even though it's almost twice as bad as the CM 1500.

On the other hand, some folks here said the CM lite takes 30-60 seconds to throw. That kinda sucks, I'd be likely to save up an extra $75 for hte 1500 based on that alone....

kcstott's main concern is accuracy, the extent to which a given measurement agrees with the standard value for that measurement.

wbunning and Whiterabbit's main concern is repeatability, the ability to display the same value when a weight is placed on a scale more than one time.

I think repeatability is more important in weighing powder charges, but the most straightforward way to confirm repeatability is to verify multiple measurements against a known standard.

Just because the dispenser displays the same number each time does not mean the same weight of powder is actually dispensed each time.

There will be random error where the dispenser throws nominally 40.0 grain charges as:
[39.9 40.1 39.8 40.0 40.2 39.9 40.1] and so on, where mean value is still 40.0.
The ES is 0.4, SD is 0.131.

There will be systematic error where a dispenser throws nominally 40.0 grain charges as:
[40.2 40.4 40.1 40.3 40.5 40.2 40.4] and so on, where the mean value is actually 40.3.
The ES is 0.4, SD is 0.131, same as the first data set.

To really compare the accuracy/precision between dispensers, one can't just rely on what value is displayed on each dispenser.

A good test would be this:

1. While the ambient temperature is low, calibrate and zero/tare each dispenser.
2. Dispense from each machine a sample of 10 charges, for example 40.0 grains of H4350.
3. Weigh each charge on a scale that is capable of 1 order of magnitude higher precision than that of the dispensers. Preferably a magnetic force restoration sensor-based scale, e.g. A&D FX-120i, OHAUS Explorer, Sartorius Entris)
4. Record the weight values and note the variations (random error and systematic error)
5. Raise the ambient temperature, and without recalibrating the dispensers, dispense samples of the same nominal weight.
6. Weigh each charge from the second sets of samples and note the variations (random error and systematic error)

[jimmykan]

Ooh, and then:

7. Recalibrate each dispenser at the higher ambient temperature and repeat.

[Whiterabbit]

I asked for 20 drops. Good enough for me.

[jandmtv]

The first day I got the lite and threw 30 charged, only 1 went over by .1gr. The rest of the 29 were checked on my gem pro and they all came in between 42.48-42.52. That’s plenty accurate if you ask me.

[jimmykan]

The first day I got the lite and threw 30 charged, only 1 went over by .1gr. The rest of the 29 were checked on my gem pro and they all came in between 42.48-42.52. That’s plenty accurate if you ask me.

Ideally, you need to check an instrument under test against another instrument that has been calibrated. This instrument should have a level of accuracy/precision of at least double that of the instrument under test (i.e. readable to 0.05 grain), and better yet would be one order of magnitude higher (i.e. readable to 0.01 grain).

Also, the Gempro scales have a tendency to drift and jump.

I will weigh a charge on my Gempro 250, it will read 42.50. I will remove and replace the pan, and it will then read 42.52. I will remove/replace again and the new reading might be 42.48

So I would conclude that the reading can only be trusted within 0.04 grains.

What really annoys me is that I will weigh the exact same charge later on the Gempro and it will read 42.70 or something.

[jandmtv]

Ideally, you need to check an instrument under test against another instrument that has been calibrated. This instrument should have a level of accuracy/precision of at least double that of the instrument under test (i.e. readable to 0.05 grain), and better yet would be one order of magnitude higher (i.e. readable to 0.01 grain).

Also, the Gempro scales have a tendency to drift and jump.

I will weigh a charge on my Gempro 250, it will read 42.50. I will remove and replace the pan, and it will then read 42.52. I will remove/replace again and the new reading might be 42.48

So I would conclude that the reading can only be trusted within 0.04 grains.

What really annoys me is that I will weigh the exact same charge later on the Gempro and it will read 42.70 or something.

[kcstott]

I’ll simply say I agree with Jimmykan and not retype nearly everything he posted.

My goal in measuring powder for my match rifle loads is as follows.

1. I want to drop a charge and have it the same or within .1 gr as the rest of the loads
2. I want to know exactly what the number on my scale represents traceable to a known NIST certified standard
3. I want my loads today to be the same as the ones I loaded last month. And the same as the ones I’ll load next month.

The only way to do this is to know for sure what your scales accuracy and repeatability is. The only way to do that is with a NIST certified mass.

[J-cat]

Ideally, you need to check an instrument under test against another instrument that has been calibrated. This instrument should have a level of accuracy/precision of at least double that of the instrument under test (i.e. readable to 0.05 grain), and better yet would be one order of magnitude higher (i.e. readable to 0.01 grain).

Also, the Gempro scales have a tendency to drift and jump.

I will weigh a charge on my Gempro 250, it will read 42.50. I will remove and replace the pan, and it will then read 42.52. I will remove/replace again and the new reading might be 42.48

So I would conclude that the reading can only be trusted within 0.04 grains.
.

And the manufacturer advertises it as such. If you need better, you have to get a scale costing five times more. A scale accurate within half a tenth of a grain for $150 is a bargain. And you really don't need more accuracy for reloading.

[jandmtv]

If all you are after is 1/10th grain accuracy, the Lite is more than capable. Using the same calibration weights before each loading session I’ll pretty much guarantee that this months charges match last months. Like I said. The 29 charges the lite threw that I checked on the gem pro were within .04gr of each other. That’s impressive for a dispenser scale combo costing $200 and more than accurate enough for loading precision ammo.

[kriller134]

[jandmtv]

Plug it in, turn it on, calibrate and leave it alone till tomorrow. Then calibrate again tomorrow and use.

[kriller134]

Plug it in, turn it on, calibrate and leave it alone till tomorrow. Then calibrate again tomorrow and use.

[jandmtv]

[kriller134]

[hambam105]

I'll have to see one of these in use before I part with my money.

A coaxial press and LE Wilson tools and Dies come first.