OnTarget Precision Bullet Group Calculator

By Barr Soltis


For most of the hunting community, a day at the range shortly before opening day is almost a ritual where more rounds are thrown downrange than at the game they hunt. Many question why their rifles are grossly inaccurate and leave in disgust. There are also the realists who accept the fact that their shooting results were not as a result of their rifle, scope, trigger or ammunition, but simply because they had not practiced during the year.

However, there is a unique group of folks who engage in the art and science of precision rifle shooting. They spend significant amounts of time at the range accessorizing and accurizing their rifles, developing the best loads possible and spending lots of money in the process. It is these folks who will benefit from the OnTarget Precision Calculator (OTPC).

The developer of the OTPC is veteran computer programmer Jeffrey Block of Colorado. Jeff has been hunting and shooting since his childhood, but in late 2006 he joined a local rifle club and added small-bore silhouette competitions to the list.

After some ammunition testing, Jeff knew that there had be a better way to analyze his results with greater precision and accuracy than through the use of calipers or rulers. In early 2007, Jeff began the development a computer program to accomplish exactly that and a year later the first version of his OTPC was released. All that is needed is a computer, a scanner (or a camera) and a shot target to precisely measure and analyze both successes and failures.

I was one of the original users of the Jeff's OTPC version (1.10) which was then and remains a free download--an incredible deal. You can't beat free, but since then Jeff has developed version 2.10 and is now charging a modest fee of $11.99 with a free 15-day trial period. With the improvements that he made to his original version, I had to get it. This is an exceptional product at an unusually low price and I have not been disappointed.

By now I suspect you are wondering how the program does its business, so I borrowed some information from Jeff's website (http://ontargetshooting.com).

OnTarget Precision Calculator v2.10

The OnTarget Precision Calculator gives the marksman a tool to accurately measure and analyze bullet hole groups in their targets. It provides measurements and information that is critical for evaluating ammunition accuracy and consistency.

It has a simple and intuitive user interface. You import images from your scanner or digital camera. Set the target distance, bullet hole size, and point-of-aim. Bullet holes are then positioned directly on top of the target graphic and information about the group is generated immediately.

Group information includes: Max Spread CTC (center-to-center), height and width, average distance to center, and group offset from point-of-aim. The calculations are based on the center of the bullet holes regardless of bullet caliber. Results are shown in either standard or metric measurements along with minutes of angle (MOA).

OnTarget v2.10 Feature List:

            Calculates: group center, maximum group spread (CTC), average distance to center, group width and height, and group offset from point of aim.

            User selectable for standard or metric measurement display and data output. All measurements are displayed in selected units along with minutes of angle (MOA).

            All project information, including the target graphic, is saved in the project file. Files can be shared between users without recalibration or adjustment.

            Target project can be printed. All target information is shown on the printout.

            OnTarget v2.10 can open .tgx file created by all previous versions of the program. Note: OnTarget v2.10 project files cannot be opened in the the free version of OnTarget v1.10.

            Zoom commands include: graphical zoom, zoom in, zoom out, fit window, and zoom to selected group. Quick zoom-to-group command added, hold down and click in the group to zoom.

            Bullet holes can be selected and edited directly. No need to start over with the group if you slightly misplace a hole.

            Pre-defined values for common target distances and bullet hole sizes along with user defined custom values.

            All settings carry over from one project to the next. No need to re-enter common setup information.

            Integrated scanner support using Micrsoft's WIA (Windows Image Acquisition) system. (Future upgrades will include TWAIN support.)

            Target image can be rotated in 90 degree increments to correct orientation.

            Imports and saves popular graphic file types. (.jpg .bmp, .tif, .png)

            User defined point-of-aim on target. Aim point is used to calculate group offset.

            User selectable group text and notes displayed in Target View, in saved graphics, and on printed targets.

            User selectable graphical elements for maximum spread, group extents, and average distance to center in Target View.

            Graphical ruler for measuring distances in Target View. Correctly scaled regardless of zoom level or graphic source.

            User selectable line thickness and color for the graphical elements of the group in the Target View.

            Entry fields for project title, date, location, name, and project notes.

            The average values for all groups in the project is calculated and displayed in the Target Info tab.

            Easy to use "Set Reference" command for defining a known distance on the target for correct scaling of calculations.

            Popup menu in Target View for frequently used commands.

            Numerous hotkey combination for frequently used commands. (Go to the Help/Help Topics menu for more information.)

            Oversized toolbars for easier use.

    There are several methods for measuring and calculating the size of a group of bullet holes in a target. These methods vary depending on the tools and equipment available but the goal is always the same: determine the center points of two or more holes in a target. Once you know the position of the center points the group information can be calculated very easily.

    Traditional Methods

    The two most common methods of measuring bullet hole groups involve the use of calipers. Both methods are used to calculate the maximum spread, or center-to-center distance, of the group. Let's take a quick look at each.

    In the first method a standard set of calipers is used to measure the extreme distance to the outside edges of the holes in the group. Then several holes are measured and an average size calculated. Finally the average hole size is subtracted from the overall measurement resulting in the group center-to-center distance.

    The second method of measurement uses a set of calipers modified to hold a pair of clear circlular templates along with an eyepiece for optical magnification. The operator looks through the eyepiece, aligns the two circles with the extreme holes of the group, and reads the center-to-center distance directly from the caliper.

    Both of these methods produce very accurate results and with practice can be done rather quickly. The first method is more commonly used, because it can be done with a standard set of calipers. The second method is used to certify groups due to its greater accuracy.

    OnTarget Method

    OnTarget uses the center of the bullet holes to calculate the group information. First an image of the target is imported. The desired bullet hole size is set along with the target distance, the point of aim and the reference distance, if needed.

    The user zooms in on the bullet holes that will be added to the group, selects the hole input tool and clicks in the Target View. A circle drawn at the defined bullet hole size is displayed and moves with the mouse. The user positions the circle over a bullet hole and clicks the mouse button to anchor the hole. As each hole is entered the group information is calculated and displayed.

    The use of the circle on the view of the target allows the user to accurately position the center point of the hole. Even if the bullet hole does not have a clean edge all the way around the circle can be positioned accurately. The OnTarget method works very well and I both use and recommend it.




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