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Patterning Your Muzzleloader: Shotgun Insight

posted Jan 4, 2011, 12:04 PM by Peter Lucas   [ updated Aug 29, 2012, 1:13 PM ]
    I do a lot of patterning of my muzzleloaders.  Generally, I will shoot at least five rounds from each gun with the intended load before using the gun for target shooting or hunting.  Since a typical load of 9 shot contains more than 500 pellets, that would be a lot of little holes to count. Rather than manually count all of those holes, I rely on some free (and very effective) software from for my patterning work.

How to Pattern a Shotgun

    Prior to getting into the specifics of the Shotgun Insight Software, some basic information regarding  shotgun patterning is helpful.  Informal patterning can be done simply by putting up a piece of paper, stepping back an adequate distance and  firing a load.  The distance you step back from the target is largely dependent on the type of shooting which will be doing.   My practice is to pattern the gun at same range as your typical shot.  This informal type of patterning will give you a pretty good idea of whether you have any big holes in your pattern and whether you have adequate pattern coverage to hit what you are shooting at.  However, the only information which get from this type of informal patterning is a general sense that your pattern looks "OK." You will not end up with any quantitative information about how your patterns compare to the accepted norms for pattern density.

    The  traditional method for obtaining quantitative information regarding pattern density was developed in the British gun makers during the19th century. The traditional way patterning a shotgun is pretty straightforward. You tack a large sheet of paper on target stand and mark the center of paper to give you an aiming point.

Average Number of Pellets per Ounce of Shot

Shot Size
Approximate # of Pellets per Ounce
8 1/2485
7 1/2350
Backing off 40 yards, you fire at the aiming point.  You next scribe a 30-inch circle around the densest portion of the pattern and count the number of pellets in that thirty inch circle.

    The pattern density is determined by comparing that to the total number pellets in the load to the number of pellets in the 30 inch circle.  In order to make this comparison it is necessary to know the total number of pellets in the load,  This  is usually estimated based on the standard size of the shot pellets.  For example, a one ounce load of Nine shot will typically have 595 pellets. The accompanying table gives the average number of pellets of shot in an ounce for the various standard pellet sizes.  However, the number of pellets per ounce can vary from manufacturer to manufacture.  If you are really particular, you will go the extra step of counting the actual number of pellets in several sample shot charges.  

Standard Choke Percentages

Choke40 yards
Skeet 50%
Improved Cylinder 55%
Modified 60%
Improved Modified 65%
Full 70%
Armed with this information, you divide the number of pellets number pellets within the 30 inch circle by the number of pellets in the load.  The resulting percentage is then compared to a set of standards to determine the choke of the gun.  For example, a modified choke, on average will produce patterns with 60% of the pellets hitting within the 30 inch circle at 40 yards.  The accompanying table list the accepted percentages for the various chokes.

    For each load you should to fire at least five patterns, and ten is even better. The average of your five or ten test patterns will give you your pattern density for that particular gun and load .  You will need to repeat this process for each load and choke you use in that gun. Obviously, this a lot of tedious work, especially when you are using small shot.  Counting three or four hundred pellet strikes per target is not really that much fun.

    While the traditional method of patterning a shotgun produces some useful quantitative information, it does have its limitations.  The raw percentage of pellets in the 30 inch circle provides virtually no information about how the pellets are distributed within the 30 inch circle.  As a result, a number of different methods have been developed for attempting to provide additional information regarding the distribution of the pellets within the core of the shotgun pattern. 

   Many of the current methods of describing the distribution of pellets in a shotgun pattern are based on the book The

A shot gun pattern showing the number of five inch patches in the 30 inch circle.
Mysteries of Shotgun Patterns
by George G. Oberfell & Charles E. Thompson, Oklahoma State University Press, 1957. Oberfell and Thompson observed that, on average, the pellet density in the center is generally greater than at the edges of the pattern. The average pellet density gets progressively less dense as distance from the center of the pattern increases. Oberfell and Thompson concluded that the the distribution pellets approximates a typical bell shaped curve which we learned about in statistics class.  Oberfell and Thompson presented a method of determining evenness based on the ability to find places where 5" circles (areas which they termed as "patches") could go into a pattern without encountering a pellet hit. Using this information and some related charts, you were able to grade the patterns into good, average and poor categories. For various reasons, this method of grading pattern distributions ever caught on.   However, the statistical modeling of shot patterns described in Oberfell and Thompson continue to be used today.

Shotgun Insight.

With the advent of digital photography and personal computers it is now possible to analyze shotgun patterns in a wide variety of ways which were not available to Oberfell and Thompson.  There are expensive patterning "machines" which use digital technology to analyze shotgun patterns.  However, if you have a digital camera, Shotgun Insight allows you to preform sophisticated analyzes of your shotgun patterns for the cost of some patterning paper.  The free software from Shotgun Insight counts the number of pellet strikes, calculates the percentage of pellets hitting in the center 10, 20 and 30 inches of the pattern, determines the likelihood of a pellet strike on a clay target and preforms a number of statistical analysis.  For most of us, the software provides more information that you really need.

The mechanics of using Shotgun Insight are straight forward.  You start by hanging a large piece of white or other light color targeting paper on a target stand.  For paper, I use rolls 36" wide paper which is intended as masking paper for painting.  The masking paper is inexpensive and available locally at both Home Depot and the local painting supply store. The paper comes in two colors, one which has a reddish hue and the other a brown hue.  Both colors of paper seem to work equally well for patterning.

    Typically, I will label each target with a number or letter on the top left corner which corresponds to the shot number in the test string.  That way it is easy to identify the different shots on the digital pictures.   For the first pattern in the test string, it is also a good idea to include information regarding the gun, the amount of powder, size and weight of the shot charge and the wad column for future reference.    It is also a good idea to put a dot in the center of the patterning paper in order to provide a reference point for aiming.

    After shooting at the target, walk down range and take a picture of the pattern.  Be sure to include some object of a known size.  In order to accurately analyze the pattern, the Shotgun Insight software will need to be calibrated using known horizontal and vertical distances.  I my case, I use the outside of the patterning target stand which measures 48x47.  You also need to pay attention to the lighting of the pattern when taking the picture.  Shadows running across the pattern will make the pictures useless.   In addition, it is difficult to get good results with the software if the sun is shining on the back of the target.  

    Once you have the picture, the paper target becomes irrelevant.  You can simply put an new piece of paper over the old one.  This eliminates the need to carry around a number of large paper targets for future analysis.   It also makes handling the paper easier, particularly on a windy day. 

     With the digital pictures in hand, the images are loaded into the Shotgun Insight software.  T
he software counts the pellet strikes (after some clean up). Shotgun Insight provides a wealth of information regarding the pattern and also creates average information for each the test patterns in the string.  The Shotgun Insight web page contains a number of screen shots from the software in action and the output which is generated. Check out the Shotgun Insight web page for more information. 

 Specific Issues with Muzzle-Loaders.
    Virtually everything so far in this Article applies equally to any shotgun; muzzle loading or modern. However, here are some specific issues which you are likely to encounter with a muzzle loading shotgun:

Blown Patterns:   A blown pattern is a pattern where the shot is not dispersed in the standard bell shaped curve.  Instead, there are few or no pellets found in the center of the pattern.  These types of patterns are sometimes referred to a having a dough-nut hole for obvious reasons.

     With today's modern shotguns, it is very uncommon to have a blown pattern.  The manufactures of shot shells and shot shell components have spent countless amounts of time and money in attempts to eliminate these types of patterns.  Consequently, with modern guns, it is necessary to to shot only enough test shells to insure that you have an adequate sampling of the patterns from a statistical perspective.  However, dough-nut hole patterns are a fairly common occurrence with heavier loads with a muzzle-loading shotgun.  The biggest problem with blown patterns is that they are not predicable.  I have experienced the situation where the load will produce four beautiful patterns in a row on the fifth shot, you get a dough-not hole.  Consequently, not only need to fire enough test shots with your muzzle-loading shotgun to obtain an adequate statistical sampling, you also need to shot enough times to satisfy yourself that your load will not occasionally throw an blown pattern. 

    There is no "correct" number of test patterns you should shoot to insure that you are not producing the occasional blown pattern.  However, you should shot a minimum of five test patterns.  If you are testing a heavy load, where blown patterns are more likely, it would be a good idea to shot ten test patterns. 
    Black Powder Fowling
:  The amount of black powder fowling in the barrel definitely has an effect on the patterns which your gun will produce.  Consequently, it is a good idea to shoot a few shots in each barrel prior to starting your test patterns.  That way you will have a more accurate sampling of the patterns which you are like to encounter under actual shooting conditions. 

    Shot Cartridges.  Finally, if you are using shot cartridges in your muzzle loading shotgun, you need to shot an adequate number of shots to make sure that your cartridges are not "balling".  Balling occurs when the cartridge fails to open the the shot charge flies down range as a single slug.   This is a very dangerous situation.  If you are going to use shot cartridges, shot at least ten test patterns before you take them into the field.