My guess is that Dr. Courtney (PhD, Physics, MIT) wanted to remove variables that are involved with the cartridge load process that would affect velocity. By using a transducer to measure the actual psi/mg, all the attendant load stuff would be skipped and an actual evaluation of primer consistency would be determined by measurement of blast pressures. Table 2 shows a bunch of primers were weighed to within .1 mg, total mass and pressures. Pressure tests using total primer mass (fig. 3) and mass loss by detonation for Fed. 210M primers, (fig. 4) were shown with weights to .1 mg. I think the study was aimed at shooters rather than engineers/scientists. If Dr. Courtney conducted this study using any grant or public funding budget considerations would be in effect.
Low velocity spreads would introduce the entire load process and environmental factors into consideration. My thinking is that velocity consistency would not be greatly affected by minute primer explosive charge variations measured in .1 mg increments because of the tiny quantity of the primer action compared to the entire load process. I liked the study, in part, because I could easily understand it and other confusing and unnecessary factors were omitted.
All this fussing over primers would be sort of negated should the carefully selected primers produce vertically strung groups ("observed on the target") having low velocity spreads and standard deviations.
Variables introduced by hand-loading cartridges affect velocity. This can never be avoided the real shooting world, so why use a method to evaluate primers that avoids such variables? It is meaningless to use a readout that has no demonstrable relation to accuracy/precision on a target. In contrast, velocity has a clear link to accuracy/precision.
As far as balances go, I learned quite a bit about them when I received my PhD in Biochemistry and Molecular Biology at Purdue University. Courtney specifically stated that he used an Acculab VIC-123 balance for this body of work. I downloaded the user's manual some time ago when I first became aware of this article, to determine whether it might be a limiting factor in the methodology employed. Courtney reported in this paper that the balance used has 1 mg readability, but that is misleading because it only has +/- 3 mg linearity, which is a better measure of the balance's capabilities for this purpose. Readability is simply the number of digits displayed on the screen and has nothing to do with the actual accuracy/precision of the balance.
Further, the values in Table 2 or elsewhere in the paper were not "weighed to within 0.1 mg". Those are
averaged values reported to number of significant digits that were simply not justified based on the equipment used. That is the major flaw that invalidates the entire work, IMO. He used a balance only capable of determining mass to +/- 3 mg, and reported the average measurement to a resolution far higher than which the instrument was actually capable. In more simplistic terms, the scale can't actually weigh what they claim it weighed. Identification of limiting sources of experimental error and spotting methodological discrepancies are something I also learned
ad nauseum while in graduate school.
The readers of any
published scientific report deserve to have confidence that what they are reading actually is scientifically valid. That is one reason why many upper tier journals use a peer review process. I have seen quite a few claims that primers can be weight-sorted to improve precision. If someone makes the claim in a post at an online shooting forum, whether with or without supporting data, well, you just have to take what you get and decide whether to believe it or not. If it is a published report, the authors have measure a responsibility to ensure that the conclusions are fully supported by experimental evidence. Given the number of competitive shooters in this country and elsewhere, the notion that primers can be weight-sorted is NOT a trivial one. In fact, given the cost, time, and effort many of us put into the sport, I'd say it's far from trivial. I would very much like to believe that weight-sorting primers can make a difference, but I'm not there yet, partially because of such unsupported claims as have made in this paper and elsewhere.