statistics. Those which describe the par- ent group are called predictive statistics. Our results will be interpreted by the use of predictive statistics. Although the groups that we shot (15 five-shot groups) yielded statistically significant results, this information tells us only about the groups fired and not what we can expect of future groups shot under the same conditions. Because of our large sample size (75), our sample specific results are very similar to the predictive statistics. The primary dif- ference between the two is that the predictive statistics uncertainty levels are usually much larger than the un- certainty of sample specific statistics. A larger uncertainty level means that the difference between two groups must be greater if they are going to be statisti- cally significant. This gives us further insurance that the results we obtained can be duplicated in the future with a high degree of certainty. .17 Mach 2 Results
Chronographed velocity data was statistically analyzed using Winks SDA
software program. Table 1 shows a typi- cal report generated by Winks SDA. This report shows how Winks SDA statisti- cally analyzed the velocity data for the CCI 17-grain .17 Mach 2 round. Since we were concerned only with compar- ing two variables — an unsuppressed .17 Mach 2 rifle and a Gemtech HMR suppressed rifle — Winks SDA did a preliminary test (equality of variance) to determine which version of the t- test should be performed. The p-value for equality of variance was less than 0.05 and therefore the unequal vari- ance two sample t-test was used. This test concluded that at the p = 0.05 level (statistically significant) the means of the two groups were significantly differ- ent. The velocity of the Gemtech HMR suppressed group (2,011.00 fps) was 11 fps faster than the unsuppressed group (1,993.00 fps). Utilizing the On Target Preci-
sion Calculator I was able to precisely measure and plot X and Y coordinates for every bullet hole. These data then were imported into a Microsoft Excel
spreadsheet and subsequently imported into GAP (Group Analysis Program). At this time, it isn’t possible to import On Target data directly into GAP. GAP then provides us with both Sample Specific and Predictive statistics for our target groups. As stated previously, I am going
to consider only the predictive sta- tistics for my results. Although GAP can provide an enormous amount of information on our target groups, we are primarily concerned with Point of Impact (POI) and group size (Average Group Width). Point of Impact is broken down into two components: Windage, which denotes whether the shot is left (-) or right (+) of the point of aim, and Elevation which denotes if the shot was high (+) or low (-) when compared with the point of aim. Table 2 shows Sample Specific and Predictive Statistics associ- ated with the CCI .17 Mach 2 Gemtech HMR suppressed group. Predictive statistics are represented as “pattern width” instead of group width because predictive statistics do not represent an
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