Twoboxer
Member
We've had several discussions about scales, and some of those have involved the question of how consistent is the RCBS Chargemaster at dispensing the targeted charge.
When working up a load, I use my Chargemaster (reads to 0.1gr) to dispense the target load, weigh the charge on an A&D FX120i (reads to 0.02gr), and adjust it to hit the target to the hundreth of a grain. Yesterday I made ammo for a 308 load workup using Lapua 100gr HPCE bullets. FWIW, here are the results:
Powder: H335
Targets: 12 from 43.2gr to 47.1gr, 0.3gr or 0.4gr apart.
Total Loads: 10 x 3 loads, 2 x 9 loads, total 48 loads.
According to the A&D FX120i, how did the RCBS Chargemaster do?
Loads within +/- 0.06gr of target = 33 or 68.8%
Loads within +/- 0.1gr of target = 41 or 85.4%
Loads not within +/- 0.1gr of target = 7 or 14.6%
When missing the target load, by more than +/- 0.1gr, how far off were they?
+0.5gr, +0.12gr, -0.12gr, -0.14gr, -0.16gr, -0.32gr, -1.04gr
Does the RCBS miss more often High, or Low?
Exactly on target: 4
Higher than target: 18
Lower than target: 26
Notes and Observations:
- Yes, I am this anal about charge weights when working up a load. To me there's little point in testing and chronoing loads separated by (eg) 0.3gr without knowing that they are in fact 0.3gr apart. It is clear to me the RCBS Chargemaster cannot do that job. Whether that matters to you is your call, and depends somewhat on your budget or perhaps your tolerance of a beam scale.
- My guess is the Chargemaster may throw more low charges because the velocity of the powder falling into the pan can cause a momentary, artificially high reading. When operating below the target, I would often see the unit dispense, display a weight, display a bit lower weight, and then start dispensing again. But I did not observe this behavior if the unit hit the target. If the reading hit the target, the dispenser and the scale seem to shut off and report the load as complete.
- The largest discrepancy (-1.04gr) occurred when the dispenser dropped a blob of powder and the display showed the weight was higher than the target, and said so. However, the actual weight was in fact lower than the target. Since this charge would have been discarded - if for the wrong reason lol - you can choose to eliminate it from the stats if you want. The RCBS reported two other charges as high; one of those was lower than reported but in fact still slightly high while the other was within 0.02gr and should have been reported as "on target". Your call again.
- Both scales were calibrated using the RCBS 2x50g check weights. After calibration, the RCBS weighed each calibration weight as 50.00g. The A&D showed one of the weights as 50.002g, as it always does when calibrated. The same pan was used and tared on both scales.
- All weighing was done with the plates clear of any residual powder. All Chargemaster calibrating/dispensing/weighing was done with the wind guard in place. The A&D was similarly protected by using its shield minus its top and operating it inside a storage cube.
- The A&D never varied from 0.00 with the empty pan on it, and -148.68gr when the pan was removed. It never needed to be zeroed, or re-calibrated during the session. The RCBS would most often display -148.7gr, but sometimes would say 148.6gr which for the RCBS I consider close enough
.. About halfway into the session the RCBS began to show different weights with the pan removed, and was re-calibrated.
- The accuracy of this comparison depends on just how consistent the more expensive A&D scale really is, and that's a question I can't really answer lol. Based on the difference in construction, price, and my use of the two units, I'm willing to believe the A&D scale. YMMV.
When working up a load, I use my Chargemaster (reads to 0.1gr) to dispense the target load, weigh the charge on an A&D FX120i (reads to 0.02gr), and adjust it to hit the target to the hundreth of a grain. Yesterday I made ammo for a 308 load workup using Lapua 100gr HPCE bullets. FWIW, here are the results:
Powder: H335
Targets: 12 from 43.2gr to 47.1gr, 0.3gr or 0.4gr apart.
Total Loads: 10 x 3 loads, 2 x 9 loads, total 48 loads.
According to the A&D FX120i, how did the RCBS Chargemaster do?
Loads within +/- 0.06gr of target = 33 or 68.8%
Loads within +/- 0.1gr of target = 41 or 85.4%
Loads not within +/- 0.1gr of target = 7 or 14.6%
When missing the target load, by more than +/- 0.1gr, how far off were they?
+0.5gr, +0.12gr, -0.12gr, -0.14gr, -0.16gr, -0.32gr, -1.04gr
Does the RCBS miss more often High, or Low?
Exactly on target: 4
Higher than target: 18
Lower than target: 26
Notes and Observations:
- Yes, I am this anal about charge weights when working up a load. To me there's little point in testing and chronoing loads separated by (eg) 0.3gr without knowing that they are in fact 0.3gr apart. It is clear to me the RCBS Chargemaster cannot do that job. Whether that matters to you is your call, and depends somewhat on your budget or perhaps your tolerance of a beam scale.
- My guess is the Chargemaster may throw more low charges because the velocity of the powder falling into the pan can cause a momentary, artificially high reading. When operating below the target, I would often see the unit dispense, display a weight, display a bit lower weight, and then start dispensing again. But I did not observe this behavior if the unit hit the target. If the reading hit the target, the dispenser and the scale seem to shut off and report the load as complete.
- The largest discrepancy (-1.04gr) occurred when the dispenser dropped a blob of powder and the display showed the weight was higher than the target, and said so. However, the actual weight was in fact lower than the target. Since this charge would have been discarded - if for the wrong reason lol - you can choose to eliminate it from the stats if you want. The RCBS reported two other charges as high; one of those was lower than reported but in fact still slightly high while the other was within 0.02gr and should have been reported as "on target". Your call again.
- Both scales were calibrated using the RCBS 2x50g check weights. After calibration, the RCBS weighed each calibration weight as 50.00g. The A&D showed one of the weights as 50.002g, as it always does when calibrated. The same pan was used and tared on both scales.
- All weighing was done with the plates clear of any residual powder. All Chargemaster calibrating/dispensing/weighing was done with the wind guard in place. The A&D was similarly protected by using its shield minus its top and operating it inside a storage cube.
- The A&D never varied from 0.00 with the empty pan on it, and -148.68gr when the pan was removed. It never needed to be zeroed, or re-calibrated during the session. The RCBS would most often display -148.7gr, but sometimes would say 148.6gr which for the RCBS I consider close enough
.. About halfway into the session the RCBS began to show different weights with the pan removed, and was re-calibrated.- The accuracy of this comparison depends on just how consistent the more expensive A&D scale really is, and that's a question I can't really answer lol. Based on the difference in construction, price, and my use of the two units, I'm willing to believe the A&D scale. YMMV.
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You are the most consistent with those tweezers then everyone else. You win!
