Originally Posted by goodgrouper
How about running a standard deviation on my ten shot string mentioned earlier?
The 3050 fps round contradicts the stipulation of uniform ammo due to the hypothetical tight neck. If I get a chance later, the remaining nine shots could be an interesting study. What SPS does is to identify units outside of process expectations, those having "special cause" influences, such as your tight neck.
The technique doesn't dictate your results, but it does give you an indication of the capability of your process. When the results don't meet expectations, it gives you a place to start looking. You also need more data than a single 10-shot string; otherwise you're in the world of sampling, which is not a corollary to SPC.
The purpose of my commentary is to establish the relationship between ES and SD under conditions of an in-control process. If the results don't follow, then external influences exist, whether they be ambient temperature, component, measuring error, or procedure.