Hysteresis with the large/heavy 230 grain projectile allowed us to quickly take size measurements within 10 (5 Degrees F) degree of stated temperature. This, we believe, is a better method than making the subject slightly biased beyond the target temperature and waiting for the target temperature to be reached, as this would lead to internal thermal differences. These tests are designed to be an in-house study that may give clues to what clinical results one can expect. In that light, it could be argued that the latter method could provide closer, real world results as the round chambered in a hot barrel would in fact, be in a state far from homeostasis. I would counter that for those non-sterile results, the tests should be done with the actual firearms used, and thus would not apply to other applications.
(Accuracy of the Reloader) Though the hand of the caliper user can make some tests "slightly subjective", these are the tools of a reloader. Thus they are pertinent to this test. Although calipers, micrometers, and reloader hands can be different, these results should still show reliable trends, especially when different products are compared side by side.
Tools used for measurement Mitutoyo Digital (Japan) .0005" Digital Calipers, Brown & Sharpe (USA) micrometer, Starett (USA) Dial Calipers, Eteckcity Lasergrip 1080 Infrared Thermometer (1 inch swath at 12 inches or 12:1).
And here is my beach cooler full of Dry Ice and Ethanol..
Multiple measurements were taken at different places on the base (diameter measurement) with both mics and calipers, looking for the highest and lowest diameters of each round.
Concentricity in it's self is most likely a moot data point, rather a good basis for quality control. The jacket material and the lead core are of very different densities; thus, the outside diameter differences between two points taken on the same bullet may be a good sign of what's going on; it might not have a bearing on a rotating projectile, as much as the density of the cross-section.
The ultimate test is what shoots the best out of your gun of course.
I rotated the projectile multiple times to take measurements. I looked for the lowest and the highest measurement for each bullet. I also factored small groups for the S.D. the compiled (averaged) them together to try and weed out outliers. I am not a mathematician but the raw data is available below.
The length measurements are also so close to perfect, that they can be effectively ruled as having a minimal effect on weight, accuracy and case capacity displacement. Because of FJM bullet construction, the highest point measured on the underside of the projectile is typically the jacket material. Thus, there is not much effective case capacity displacement or balance issues, it's more of a quality control test (if it possesses any effect at all on secular operation). Some length measurements were left out because the "flashing" or jacket burrs prevent a reliable measurement. (As is the case with most HP projectiles.) The flashing on the base of the bullets causes some overall length differences in the measured numbers, again this is more of a quality control index not the end all be all of tests.
The projectiles were taken from room temperature (70F) to -50C (Dry Ice in Ethanol) at about 5C/Minute from the core (best estimate) and measured. The projectiles (same ones) were then allowed to warm slowly back to room temperature, then heated to 400F at about 3F/Minute, then measured.
Reading the Data: The Highest 0-Delta-Count is the most projectiles from the same test lot, that were within .0005" of each other. The Lowest Max-Delta is the lowest measurement of the highest difference in measurement. This is an interesting number because some projectiles beat others at different temperatures.
Highest 0-Delta count at room temperature diameter = Hornady
Lowest Max-Delta at room temperature diameter = Hornady
Lowest High-Diameter at room temperature = Hornady
Highest Low-Diameter at room temperature = Both .4500"
Lowest Length delta of test group at room temperature = Sierra
Highest 0-Delta count length of test group at room temperature = Sierra
Highest 0-Delta count at low temperature diameter = Sierra
Lowest Max-Delta at low temperature diameter = Hornady
Lowest High-Diameter at low temperature = Hornady
Highest Low-Diameter at low temperature = Sierra
Lowest Length delta of test group at low temperature = Sierra
Highest 0-Delta count length of test group at low temperature = Sierra
Diameter - High Temperature
Highest High-Temperature Same-Diameter count = Hornady
Lowest Max-Delta of test group high temperature = Hornady
Note: Over half of both the Hornady and the Sierra leaked some type of flux when brought to 400F. The Extreme bullets, as they are totally plated, did not. Further, around 25% of both the Hornady and Sierra FMJRN projectile cores separated from the jacket. Not in the cold as I would have expected, but in the heat. All three of the projectile groups, after they were thermally cycled, looked to be of very different jacket alloys (and I'm sure of different core alloys, though I do not know). The Extreme Bullets stayed "shiny" through all tests, the Sierras turned to a "matte finish" in the oven, and the Hornadys turned to a "matte finish" when they were taken out of the oven, right before our eyes.
Other Observations: It became apperent (from these non-scientific tests) that Hornady maintains diameter over length and Serria puts priority on length over diameter.