A fast first shot inflates velocity SD
The same 21 strings, with shot 1 kept in and taken out. Removing shot 1 lowers the within-string velocity SD for every powder listed.
These are the same 21 strings as the first-shot chart: strings of 3 to 5 shots from a .223 Savage Axis II. The figure is the pooled within-string velocity SD, once with shot 1 included and once with shot 1 removed. AI was used to recompute each recorded string both ways and pool the results. The values below are the ones in the session notes.
- N140: 28.9 fps with every shot, and 24.3 fps with shot 1 removed.
- Varget: 28.3 fps, then 22.1 fps. Varget is only 2 strings.
- N133: 31.1 fps, then 26.4 fps.
- IMR 8208: 25.8 fps, then 22.8 fps.
- CFE 223: 31.2 fps, then 30.2 fps.
The fast first shot inflates the SD by about 1 to 6 fps for every powder in this set.
The notes’ caveat: the strings are short, and Varget is only 2 strings. A lower SD after dropping shot 1 describes these 21 strings.
These are recorded session numbers, not a recommended load. See the Safety page.