Chargemaster 1500 accuracy

[PhilC]

Years ago I ordered a small brass insert from ebay, which worked better than the straw for me.

I got a brass insert too, don't recall if from same source or elswhere works very well.

 

[ebb]

I've been using a 1500 since about a year after they came out and was pleased with it until about a year and a half ago. I found that some throws were off a lot. Asked here and found the biggest issue is static electricity. RCBS says to wipe with dryer sheet or antistatic cloth every time you use it. What have you guys done about static elec.? I bought a little kit that I can adapt to ground the 1500 in an electrical out let using the ground plug.

 

[Ron Gorski]

My Chargemaster is probably close to 15 yrs old. I am running the modified settings published here many years ago that were provided by the RCBS rep.

I usually have very good SD/ES with my Chargemaster thrown loads.

Had some time today to perform a test.

30.0 gr Varget setting. 100 throws. Not a single overthrow.

Chargemaster and FX120i both warmed up for around 12 hrs.

I was a little surprised at the accuracy but it explains the good results that I have experienced.

Low 29.93
High 30.07
AVG 30.01
SD 0.0434
ES 0.14



There was only one 29.93 and only one 30.07. If I throw those out:

SD 0.04
ES 0.12

That is not accuracy. That is repeatability.

 

[kelbro]

That is not accuracy. That is repeatability.

Actually, it was both. The majority of throws (72%) were at 30 grains +/- .05 grains. None of the throws were outside the published (+/- .1) spec. That's both accurate and repeatable.

 

[Ron Gorski]

Actually, it was both. The majority of throws (72%) were at 30 grains +/- .05 grains. None of the throws were outside the published (+/- .1) spec. That's both accurate and repeatable.

One must check Uncertainty of measurement (accuracy) with a known good (calibrated) check weight. Just because the 30 grains were inside the +/-0.1 grain spec doesn't mean the scale was accurate.

 

[sgav8r]

Actually, it was both. The majority of throws (72%) were at 30 grains +/- .05 grains. None of the throws were outside the published (+/- .1) spec. That's both accurate and repeatable.

I personally wouldn’t consider +/- .05 to be “accurate” when dispensing Varget. That’s about a 5 kernel variance, from load to load.

Just because your CM can do that repeatably, does not make it “accurate”. An AutoTrickler will get you +/- .02, a 2 kernel variance, considerably more accurate.

 

[Straightshooter1]

I've been using a 1500 since about a year after they came out and was pleased with it until about a year and a half ago. I found that some throws were off a lot. Asked here and found the biggest issue is static electricity. RCBS says to wipe with dryer sheet or antistatic cloth every time you use it. What have you guys done about static elec.? I bought a little kit that I can adapt to ground the 1500 in an electrical out let using the ground plug.

I never let powder sit in my 1500 after my charging session. So, when I drain all the powder out I put a couple used dryer sheets in the canister (on occasion wiping the insides) and let stand until the next use. I've never had an issue about static electricity with it.

BTW: One other thing I do when using my 1500 is that I use a battery to run it.

 

[kelbro]

One must check Uncertainty of measurement (accuracy) with a known good (calibrated) check weight. Just because the 30 grains were inside the +/-0.1 grain spec doesn't mean the scale was accurate.

I have 30gr check weights.

I managed NIST certified cal labs for many years. I'm quite familiar with the differences between accuracy, precision, and repeatability.

 

[kelbro]

I personally wouldn’t consider +/- .05 to be “accurate” when dispensing Varget. That’s about a 5 kernel variance, from load to load.

Just because your CM can do that repeatably, does not make it “accurate”. An AutoTrickler will get you +/- .02, a 2 kernel variance, considerably more accurate.

For 1K loads, I use the CM to throw just short of my desired weight and trickle with the Dandy. I get 0 variance (within the scale's tolerance) and 0 overthrows. A little slower but still more 'accurate' than an Autotrickler.

 

[Straightshooter1]

For 1K loads, I use the CM to throw just short of my desired weight and trickle with the Dandy. I get 0 variance (within the scale's tolerance) and 0 overthrows. A little slower but still more 'accurate' than an Autotrickler.

I feel that's the best way to go about getting a consistent result. Likewise, I would throw short and trickle up. Though my trickling method was a little different. Since I used a clear straw and regulated the flow of powder through the straw, I'd have the CM throw short and as I could see the few powder kernels sitting on the edge of the straw, I'd just lightly tap the CM cylinder to trickle up as needed. Without being able to regulate that flow, there'd be way to many kernels bunched up sitting on the edge waiting to drop in order to control the trickle.

 

[wkdickinson]

I used a CM 1500 for probably 8 or 9 years. I was always suspect of the rounding algorithm they used. I did the the "settings" thing and built my own "nozzle" instead of the straw and all those things helped. When I bought a AutoTrickler V4, I did several studies (50 throws min) comparing the accuracy of the CM1500 scale, comparing the throws to the weight on the A&D FX120i (I only used throws from the CM1500 that were exact). What I found was that most were within the 0.10gn range, per the CM 1500 spec. But there were also far too many in the 0.20gn range.

 

[L.Sherm]

But there were also far too many in the 0.20gn range.

That .20 will absolutely throw a flyer in cartridges that use 35.0 and under.
It could also put you over max in smaller cartridges.

 

[Doom]

It helps to understand some things about the 1500 (and this includes all RCBS and other single tube dispenser units). The first thing to understand is that the displays are not the limiting factor on precision in automatic dispensing. The scales are more responsive electronically. The reason for the limited display is cost and also issues related to the dispensing issues.

The issues with repeatability are numerous and are a compromise. The first compromise is that the unit is expected to dispense powders with a VMD (cc/grain) of about 0.14 to about 0.65 through a single tube at fixed RPMs. In essence the tube is a fixed volume device, This is more than a two to one ratio. This affects the amount of material dropped by weight for every revolution of the tube. Because the scales use load cell technology the sensitivity of the scale has a fairly long time constant (response time) that has to be accounted for in the control of the dispenser. as well as the averaging time of scale display reading. The load cell is used for cost reasons. The display resolution is sufficient for the expected degree of precision of the dispenser and is a cost factor.

In operation the dispenser drops powder from some height above the platen/pan/powder surface which means it has velocity when it hits the pan. That velocity is energy that shows up as weight when the pan stops the kernels. The controls for the dispenser must wait for this reading to stabilize before it decides to either stop the dispenser and decide on a good charge or declare an overthrow/underthrow or to trickle another time.

Underthrows and overthrows are due to the same problem. Underthrows occur when the devices wants another trickle but too much weight is dumped, the scale doesn't have time to settle and thinks the charge is correct and decides to stop the process. The scale then settles below the setpoint range. An overthrow occurs when the dispenser needs a small trickle charge and the tube dispenses too much.

So in the case of the 1500 the first modification is the infamous straw or bushing. Both methods work to reduce the size of the trickle charge. The straw removes the threading in the tube to reduce the clumping of the powders. The bushing approach reduces the volume by reducing the area of the tube outlet. The programming mods work in conjunction with tube mods by reducing the amount of powder packed in the tube (slower speed for longer periods of charge) to reduce the amount of powder at the outlet of the tube.

The Chargemaster Supreme has some added capability to adjust the times built into it by running some test charges and adjusting the loads where the speed is changed.