Using a GEMPRO-250 to check a ChargeMaster 1500

[MCMXI]

There are quite a few reviews out there for the GEMPRO-250 such as this one.

http://www.accurateshooter.com/gear-reviews/gempro-250-digital-scale-review/

I ordered one last week and received it on Friday. I plugged it in, let it "warm up" and calibrated it using the included 20.000 gram check weight. I then checked the scale using Lyman check weights that I've had for a while. Those Lyman weights were checked using a Mettler XP504 which is a lab grade scale. I then checked the weights of ten loads of 43.4gr of Reloder 17 dispensed using one of the ChargeMaster 1500 units with all ten showing 43.4gr on the CM. Here are the results with the associated errors.

43.36 > -.04
43.38 > -.02
43.40 > .00
43.42 > +.02
43.38 > -.02
43.46 > +.06
43.38 > -.02
43.44 > +.04
43.38 > -.02
43.40 > .00

Overall that's not bad for the CM which dispensed that particular powder to within +.06gr to -.04gr. The resolution of the GEMPRO-250 is 0.02 gr so that's why there are no odd numbers at the end of the measured weights. Reloder 17 has fairly large kernels so I plan on doing another test using Varget, N540 or H1000.

Note: The GEMPRO-250 manual has a confusing paragraph pertaining to accuracy.

"The GEMPRO-250 has two Carat modes. One reads in 0.001g/0.005ct increments and the other reads to 0.002g/0.01ct. This was done so that jewelers can choose which accuracy they require for their use. We suggest to use 0.002g/0.01ct when possible for maximum accuracy."

This is counter intuitive. I would think that the smaller increment would be more accurate or perhaps I mean precise.

 

[Rule3]

I "guess" the question is, when loading around 43.0 grains of powder how much does 2/100th t0 4/100 of a grain matter??(throwing out the low of .00 and high of .06)??

 

[MCMXI]

Good question ... and I don't know yet. Based on a number of 5-shot groups at 100 yards in the 0.250 moa range, it doesn't matter much at all. However, the velocity spread of those groups indicates a potential issue at longer ranges. I conducted a test yesterday along the lines of taliv's suggested experiment in the link below but the results were terrible, so I have doubts about my methods.

http://www.thehighroad.org/showthread.php?t=750338

 

[Rule3]

Well you guys shoot farther than I take a plane trip!

 

[Sniper66]

I checked my Chargemaster many times with balance scales and with weights and found it to be very consistent. I appreciate your post . Good info!

 

[Reloadron]

You have one in there 43.46 > +.06 which if resolved to 0.1 gn would actually be 43.5 gn all of the rest would resolve to 43.4 gn. I define resolution as the ability to read an instrument or of the instrument to be read with resolution and accuracy being two different terms having two different definitions. I see precision as a measure of repeatability and accuracy I define as unbiased precision. That said it resembles this cartoon:



As to the scales in general. There was a time when a manufacturer stated the accuracy usually as some measure of uncertainty and also stated the resolution. Most scales we use for reloading anymore seem to state the resolution and that is also the uncertainty of the scale.

What this really comes down to is when loading ammunition how much resolution and accuracy do we really need. Seems like forever +/- 0.1 gn was adequate. Then long range shooters began to move towards jeweler type scales or more accurate and higher resolution scales. We know there is no secret or magic to making very accurate ammunition. I believe in a word we all agree "Uniformity" is the key word. Volume of the brass, bullet weight and concentric bullets, flash hole uniformity, neck tension, powder charge and finally along with things I haven't mentioned we have the primer responsible for a clean uniform ignition of the powder charge. So which weighs the most in a quest for accuracy? How much will a variation in the powder charge matter if every single primer flash is not absolutely uniform? Just looking at these Primer Flash Test Photos I have to wonder within any given lot how uniform the primer brisance is primer to primer and what the overall effect is? Does it negate being able to resolve a load out to 0.02gn for example?

Then the matter of test weights or calibration weights. Good weight sets are divided by classes and the only way to check a good scale is using a good weight set.

Once nicer and drier weather moves in I hope to get more over the chronograph. Today, the first day of Spring in true NE Ohio fashion it lightly snowed with cold!

Ron

 

[cali_blues]

...

Note: The GEMPRO-250 manual has a confusing paragraph pertaining to accuracy.

"The GEMPRO-250 has two Carat modes. One reads in 0.001g/0.005ct increments and the other reads to 0.002g/0.01ct. This was done so that jewelers can choose which accuracy they require for their use. We suggest to use 0.002g/0.01ct when possible for maximum accuracy."

This is counter intuitive. I would think that the smaller increment would be more accurate or perhaps I mean precise.

I too was baffled by that paragraph in the manual for my gempro. I asked Will Knott Scales where I bought it, and they said .001 mode is the most accurate. So that is the mode I use. Maybe it is just a typo, but man that is a pretty serious typo.

 

[lightman]

I love my Chargemaster! Its good to see that it really does have an acceptable level of accuracy. I have always had doubts that anyone can shoot the difference between .001 grain. Thanks for posting this.

 

[Rule3]

How much will a variation in the powder charge matter if every single primer flash is not absolutely uniform? Just looking at these Primer Flash Test Photos I have to wonder within any given lot how uniform the primer brisance is primer to primer and what the overall effect is? Does it negate being able to resolve a load out to 0.02gn for example?



Ron

I find the above part the most interesting as it relates to another thread on changing primers and how it may change accuracy. I know this post is about the scales, but the primer flash pictures is very telling (sort of)

As you say is every primer the same consistency? what can we tell by one picture of a individual primer? Are they made the same as when the picture was taken?? If based on the one picture, folks would think the Remington (LR) or perhaps the RWS would be almost nuclear! Those pictures are over 12 years ago, so how do they compare to today??

I have e mailed Federal and CCI in the past and they really do not or will not say anything about their primers. I asked Federal mainly about if they tested theirs compared to others and can they state that theirs are more sensitive (mainly handgun) Does the premium primers "hand made" by experienced workers really make a difference?? I can not imagine in the production of millions of tiny primers
They package them in large containers with more space between them but the company will not verify why, just that is was regulation (we "assume it is because they go bang easier,to prevent chain firing, which they may well do) but Federal is tight lipped.

That said I believe there are other factors the change the load far more than ,02 grains of powder,

 

[Reloadron]

I find the above part the most interesting as it relates to another thread on changing primers and how it may change accuracy. I know this post is about the scales, but the primer flash pictures is very telling (sort of)

As you say is every primer the same consistency? what can we tell by one picture of a individual primer? Are they made the same as when the picture was taken?? If based on the one picture, folks would think the Remington (LR) or perhaps the RWS would be almost nuclear! Those pictures are over 12 years ago, so how do they compare to today??

I have e mailed Federal and CCI in the past and they really do not or will not say anything about their primers. I asked Federal mainly about if they tested theirs compared to others and can they state that theirs are more sensitive (mainly handgun) Does the premium primers "hand made" by experienced workers really make a difference?? I can not imagine in the production of millions of tiny primers
They package them in large containers with more space between them but the company will not verify why, just that is was regulation (we "assume it is because they go bang easier,to prevent chain firing, which they may well do) but Federal is tight lipped.

That said I believe there are other factors the change the load far more than ,02 grains of powder,

When I initially really got into all of this was over 20 years ago and I decided if I overly pursued it I would either go blind or become OCD before we knew what OCD really was.

I won't drift off too much on primers but yes, sometimes the cake mix is a secret or propitiatory.

As to scales? When I want to check the uncertainty I use good check weights. I have several scales but my main weighing system now is a RCBS Chargemaster and I am real happy with the results it gives me. Then too, I am limited at my regular outdoor range to 200 yards. If I am not mistaken member bds bought a good set of test weights when we had an extensive thread on digital verse analog scales.

Ron

 

[Rule3]

I am OCD. old and going blind (well actually the old Sun in my eyes) More of a Pistolero than anything over 100 yards with a rifle.

 

[jmorris]

Now go find a few different measures and see if they can drop 10 charges of Reloader 17 and see how much they vary.