Kernel of powder accuracy

[Unclenick]

Keep in mind that while that will give you 1 kernel resolution, one kernel accuracy and one kernel repeatability are two other matters. It sounds like you addressed the repeatability by cleaning the knife edge and ways. I have not had great luck doing that. I usually find there is still a little hysteresis in the scale (pointer doesn't stop in exactly the same place when settling from below as is does settling from above). There was a fellow doing RCBS (and others, I assume, as they are all made by the same one or two OEM makers, AFAIK) scale mods to eliminate that and increase resolution, but I don't know what he did, exactly. One can imagine someone with precision grinding tools could improve knife edge and notch geometry precision, but he'd need to know exactly how far he could go, as an overly sharp edge would not hold up to the load.

Accuracy is another matter. It requires the counterweights on the beams and the errors in their notch positions all to have a cumulative inaccuracy of less than 0.01 grains. To avoid cumulative error, all that has to be tighter than the standard class 6 check-weights sold for reloading scales are. Those have a tolerance of 2 mg or 0.03086 grains for weights 10 g (154.3236 grains) and smaller, so their not good enough at this resolution level. But then, given that load sweet spots have a flat spot in a 300 yard Audette ladder, you probably don't need better accuracy than you have. It's just the consistency issue that matters.

[hounddawg]

if I think the scale is sticking I gently bounce the beam a couple of times. If it stops in a different place each time I know the knives and ways need cleaned. Cleaning should be done before leveling and checked periodically once leveled to ensure that after each bounce the needle comes back to the zero with weight on. Another thing to check is to make sure the knives are centered and not rubbing against the end caps on the ways.

If it is level and clean the accuracy of the measurement depends on how precise the machining of riders (adjustment weights) and how precise the grooves in the beam are. Once leveled and cleaned the repeatability should be spot on. All of this depends on the elimination of any paralax errors when reading the scale which is accomplished by extending the pointer and using a camera of some sort to read it with.

I am the first to admit I have no idea accurate the measurement is, that would depend on how precise RCBS was in manufacturing the riders and the beam. However that being said I have a high degree of confidence in it's precision meaning that each measurement is very close to the previous measurement. Much more precise than I can get with any electronic that uses load cells. Honestly I could care less if the charge is 41.01 or 41.03 grains as long as each and every load is the same.

I guess if you think the knives are damaged you could use a extra fine diamond hone if you have a steady hand or polish with rubbing compound to clean them up. Mine were good as they came from the factory and I would be very hesitant to mess with them but polishing using a leather strap and a bit of jewelers rouge should not hurt. Just make sure not to change the angle or dull them

[jugornot]

I have weight sorted 30 Lapua Palma 308 cases. I will do the same when my bullets show up Friday. New load test using scale to the fullest. Would rather change 1 variable at a time but way to much time. I guess next I'll save up for neck turning if I can't satisfy myself.

Bill

I used my 30 round test shots today. Everything was weight sorted and brand new Lapua 308 Palma brass. I lost one 3 shot series 44.6 due to operator error. The results are fairly encouraging. This test series will represent my zero baseline. And the results:

Series 11 Shots: 3
Min 2687 Max 2711
Avg 2701 S-D 12.4
ES 24

Series Shot Speed
11 1 2705 ft/s
11 2 2711 ft/s
11 3 2687 ft/s
---- ---- ---- ----
Series 12 Shots: 3
Min 2713 Max 2726
Avg 2719 S-D 6.4
ES 13

Series Shot Speed
12 1 2713 ft/s
12 2 2719 ft/s
12 3 2726 ft/s
---- ---- ---- ----
Series 13 Shots: 3
Min 2722 Max 2727
Avg 2724 S-D 2.4
ES 5

Series Shot Speed
13 1 2727 ft/s
13 2 2724 ft/s
13 3 2722 ft/s
---- ---- ---- ----
Series 14 Shots: 3
Min 2724 Max 2745
Avg 2737 S-D 11.3
ES 21

Series Shot Speed
14 1 2745 ft/s
14 2 2724 ft/s
14 3 2742 ft/s
---- ---- ---- ----
Series 15 Shots: 3
Min 2749 Max 2768
Avg 2756 S-D 10.1
ES 19

Series Shot Speed
15 1 2752 ft/s
15 2 2768 ft/s
15 3 2749 ft/s
---- ---- ---- ----
Series 16 Shots: 3
Min 2776 Max 2780
Avg 2778 S-D 2.0
ES 4

Series Shot Speed
16 1 2780 ft/s
16 2 2779 ft/s
16 3 2776 ft/s
---- ---- ---- ----
Series 17 Shots: 3
Min 2773 Max 2780
Avg 2776 S-D 3.6
ES 7

Series Shot Speed
17 1 2773 ft/s
17 2 2777 ft/s
17 3 2780 ft/s
---- ---- ---- ----
Series 18 Shots: 3
Min 2786 Max 2811
Avg 2796 S-D 13.2
ES 25

Series Shot Speed
18 1 2786 ft/s
18 2 2791 ft/s
18 3 2811 ft/s
---- ---- ---- ----
Series 19 Shots: 3
Min 2799 Max 2821
Avg 2809 S-D 11.1
ES 22

Series Shot Speed
19 1 2821 ft/s
19 2 2807 ft/s
19 3 2799 ft/s
---- ---- ---- ----

I also took the average changes and subtracted them from each series and came up with a SD of 8.