10.4 Interpretation of Data

Once statistics are calculated, the meaning of the result is subject to interpretation. The value of this interpretation will depend largely on the experience of the analyst, as well as the understanding of the measurement made. The meanings of each value computed by ShotStat may not be so great by themselves, but are best used together to give an overall impression of the data.

For this discussion, and the brief examples given in the General Examples section, it is assumed that all variations of bullet impact from true theoretical point of aim are described by the following physical properties:

1. side wind effect between muzzle and target
2. bullet stabilization characteristics (for example, distance from muzzle that stabilization occurs, time or distance that it takes during stabilization, degree of stabilization, etc)
3. barrel vibrations, either planer or torsional
4. muzzle velocity variations
5. deceleration characteristics (drag, head or tail wind, etc)
6. optics (refraction, mirage, parallax, etc)

In this discussion, we further assume that there is a true point of aim, defined by the bore of the firearm and not by site alignment. If we know the drag parameters of the bullet and its muzzle velocity and assume there are no optical effects, a perfect bullet (stabilized completely at the muzzle), no wind and a perfectly stiff barrel, we can calculate the impact point for a certain site picture. Further, if the sites are parallel to the bore axis in both windage and elevation directions, this calculated impact point would match the true theoretical impact point. For the case that the true point of aim is the same as that given by the actual site picture, we will say that the sites are neutral. Neutral sites are those whose site picture gives the true, theoretical point of impact. All of the General Examples assume neutral sites.

Data collected as a function of range-to-target can be extremely informative. A tiny group, artificially adjusted to zero at 100 yards, does not necessarily mean accurate shot placement at 300 yards. Plotting the standard deviations or averages calculated with ShotStat as a function of range-to-target can show a tremendous amount about actual load performance.

If a strain gauge is available, interesting correlations may exist between pressure-time curve parameter statistics (peak pressures, distribution width, etc). ShotStat can be used to compute these statistics using the Keyboard Entry function.