denton
Member
Once again, the curiosity gene stirred, leading me on another investigation.
I have a couple of old jars of Accurate 2520. In past tests, 55 grain bullet 223/5.56 loads reached a plateau beyond which more powder did not yield more muzzle velocity. Since components are in short supply, I wondered if I could concoct a load that was not troubled by the plateau, and that would be good fodder for my M4gery. And it would be especially nice if the load did not require magnum primers, since I have plenty of standard small rifle primers and fewer magnum primers.
The test involved shooting matched pairs of 62 grain bullet cartridges over the range of interesting loads, from low 223 loads to a bit into 5.56 territory. One cartridge in each pair used a standard CCI 400 primer, and the other used a magnum CCI 450 primer.
Here are the data:
The good news is that neither load reached a plateau. If there is a plateau with this bullet, it is somewhere beyond 27 grains of powder. I can use standard or magnum primers throughout the range.
The interesting discovery is that there is no detectable difference between the MVs of cartridges with standard primers and those with magnum primers. It would also be reasonable to infer that there is no difference in peak pressure.
If you take the difference between each CCI 400 point, and the matching CCI 450 point and then average those numbers, the CCI 450 shows an average advantage of 3 FPS, which is so small as to not be distinguishable from normal random variation, i.e., not statistically detectable.
Here is the analysis of the data:
Notes: Cartridges fired in random order, to wash out any effects of temperature, fouling, etc. In my old data, when MV stops increasing, so also does peak pressure. MV data captured with Labradar. Ambient temperature 68 F. Beautiful day at the range.
I have a couple of old jars of Accurate 2520. In past tests, 55 grain bullet 223/5.56 loads reached a plateau beyond which more powder did not yield more muzzle velocity. Since components are in short supply, I wondered if I could concoct a load that was not troubled by the plateau, and that would be good fodder for my M4gery. And it would be especially nice if the load did not require magnum primers, since I have plenty of standard small rifle primers and fewer magnum primers.
The test involved shooting matched pairs of 62 grain bullet cartridges over the range of interesting loads, from low 223 loads to a bit into 5.56 territory. One cartridge in each pair used a standard CCI 400 primer, and the other used a magnum CCI 450 primer.
Here are the data:
The good news is that neither load reached a plateau. If there is a plateau with this bullet, it is somewhere beyond 27 grains of powder. I can use standard or magnum primers throughout the range.
The interesting discovery is that there is no detectable difference between the MVs of cartridges with standard primers and those with magnum primers. It would also be reasonable to infer that there is no difference in peak pressure.
If you take the difference between each CCI 400 point, and the matching CCI 450 point and then average those numbers, the CCI 450 shows an average advantage of 3 FPS, which is so small as to not be distinguishable from normal random variation, i.e., not statistically detectable.
Here is the analysis of the data:
Notes: Cartridges fired in random order, to wash out any effects of temperature, fouling, etc. In my old data, when MV stops increasing, so also does peak pressure. MV data captured with Labradar. Ambient temperature 68 F. Beautiful day at the range.
