Silent Hunter — Conclusion:
Testing And Evaluating Rimfi re Suppressors Dane Hobbs
and precisely measure and analyze bullet hole groups. On Target is simple and easy to use by following these steps: 1. Import images from your scanner or digital camera. 2. Set the distance to the target (50 yards in our case). 3. Hole size (.224" in our case).
O
4. Diameter of target (3" targets were used). 5. Set point of aim (center of target). 6. Input bullet holes. 7. After five bullet holes have been measured and
recorded (since I am using fi ve shots per group) select new group and continue until all groups have been fi red. 8. The following analyses will be displayed: 1.) Maximum Spread (CTC = Center to Center). 2.) Average to Center. 3.) Group Width. 4.) Group Height.
5.) Group Offset Horizontal. 6.) Group Offset Vertical. 9.) The above information is generated for each group
as well as the target (all groups combined). Target analysis allows the data (all 15 fi ve-shot groups) to be analyzed as if it were one large group (which it is, as long as none of the parameters are changed). We could fi re all 75 shots into one target, but it would be diffi cult to input each shot since many will overlap each other. Firing only fi ve shots on an individual target makes it easy to input each shot into our software. Although On Target (Target 1) is the best and easiest
to use when measuring target groups, I prefer to export the data into a spreadsheet such as Microsoft Excel. These data are in the form of X and Y coordinates. Each bullet hole has an X coordinate (horizontal distance from the aim point) and a Y coordinate (vertical distance from the aim point). These data are subsequently imported into the GAP (Group Analysis Program) software. GAP, developed by an experi- mental physicist, is a true scientifi c target analysis program. GAP enables a shooter to perform much more complete and sophisticated analysis that entails complicated mathematical computations. GAP incorporates statistics and sophisticated mathematics that tell research scientists whether their results are statistically signifi cant or not. Unlike other target analysis programs, GAP tells you how accurate and repeatable your results are. Without this feature, your results are almost meaningless. GAP is extremely useful to those shooters who are trying to determine how accurate their rifl es are and those trying to develop accurate loads. In addition, GAP offers predictive statistics that will calculate expected future groupings as well as future shot placement probabilities. Of course, the more shot data that you supply, the more accurate your results will be. Two or three groups will provide you
n Target Precision Calculator is a free downloadable software program that enables you to consistently
with somewhat limited useful data. Since neither of the programs mentioned above incorpo-
rate velocity data, I use WINKS SDA software. WINKS SDA is a statistical analysis software program used by researchers, scientists, and stat students for determining the accuracy of their results. After I chronograph my velocity data, I enter these results into Excel, a spread sheet program. The velocity data from Excel is easily imported into WINKS. WINKS will then determine if the velocity of each variable is signifi cantly different from each other. GROUP SIZE
Extreme spread, also called Center to Center (CTC) is
the most widely recognized statistic for measuring group size. Extreme spread refers to the distance between the two most widely separated holes on the target. This is a very poor and inaccurate statistic for measuring group size. Extreme spread is actually describing the distance between the two lowest probability points (holes) on the target. This results in wildly varying group sizes that essentially should be the same. It is also why legitimate shots are eliminated as “fl yers.” It is impossible to do a target analysis using extreme spread with any level of precision. A much more accurate way of describing group size
is the average radius or the average distance from center. Although average radius provides us with more useful information than does extreme spread, it is still inferior to group width. Average radius does not provide any informa- tion in regard to the specifi c shape of a group nor is it able to distinguish between changes in shape and size. The shape of a group can provide as much useful information as the size of the group. Although most people perceive a target group as round
in nature, they generally are elliptical in shape. Group width describes the target shape in terms of major and minor widths. The longest dimension of the ellipse represents the major width and the shortest dimension is called the minor width. I will talk about our results in terms of average group width. Average group width is defi ned as the average distance of this ellipse from the center of the group. This is not the same as the average of the major and minor widths, although this value is usually very close to it. The average group width statistic is routinely used in scientifi c data analysis because it is completely objective. SAMPLE SPECIFIC VS. PREDICTIVE STATISTICS
When a target group is fi red, it is considered a sample of
the parent group. When another target group is fi red, under the same conditions as the fi rst group, it also is considered a sample of the same parent group. The parent group represents the grouping that you would get if an infi nite number of shots were fi red under the same conditions. The statistics which describe a specifi c target group are called sample specifi c
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