This page explains the basic patterning process and what to do with the data. For functionality of the software apps please go to those pages.
This process provides the following data:
1. POI – point of impact, How far off was this shot from the aim point or target center. Components of this are:
a. Windage – The horizontal offset of your shot reported in inches.
b. Elevation – The vertical offset of your shot reported in inches. Many shooters consider 3 or 4 inches high at 40 yards to be ideal.
c. Pattern Offset – The total distance from the aim point reported in inches.
2. # pellets on the target – All the pellets that hit the target. This is normally not the number within the shell; however you may try to determine this by taking a closer shot to capture all pellets while not putting a big hole in the center.
3. # pellets within a circle (30,20,10, and custom). Many standard parameters are derived from this.
4. Pellet Density is the pellets per square inch within the specified circle. This is similar to % efficiency when evaluating “kill zone”. For a given animal or clay, the pellet density of a region can be interpreted for a success ratio. An example would be that turkey hunters want to see 100 pellets in a 10 inch circle. That translates to a density of 1.273 pellets / square inch. By adjusting the custom circle feature, hunters can see where that density falls off.
5. Shot Ratio is the % of pellets above the aim point over the % of pellets below. Though this is redundant to POI, it is a very common method of communicating vertical offset of a choke or choke setting in the trap and skeet communities. Many shooters like to have a positive %, because they want to put the bead under the clay or bird.
6. % Efficiency = (# of pellets in a 30 inch circle at 40 yards) / # pellets in the shell. The user needs to enter the # of pellets in the shell, otherwise % Efficiency will be incorrect. This number is normally determined by opening 5 shells and counting each to determine an average. Enjoy. There is a shell estimator software. It has also been suggested that shooting a target at a medium range without clustering pellets too tightly will give you a useable value. Another interesting phenomenon, is that many shell manufacturers seem to have more pellets for a given ounce/pellet size than we calculate. Our assumption is that they prefer to have slightly undersized shot and slightly high count so that the patterns compare better when you look at holes in a target. Just an assumption, buy me a beer and I will gladly argue the with you.
7. Target Distance (and Analysis Distance – Target Distance is the end of the gun barrel to the target. The Analysis Distance should normally be set to the same to get “real” results that are not estimated. Analysis Distance is on the iPhone only and should be used with discretion. It allows you to set it slightly off from the Target Distance to give a relative result of performance. It assumes the pellets will travel straight from the gun on straight lines and does not account for ballistic travel, wind, in flight collisions, or pellet imperfections. Feel free to comment on its value or anything else that you prefer to see.
Patterning a shotgun is no longer hard to do. Because it was a manual process for so long, you will find many descriptions of the process that shortcut “Best practices”. People try to shoot at smaller targets and use “ball park” evaluations to avoid the tedious task. For these reasons, there are many tutorials on the internet that should now be outdated. Please see the links page for some of the many individuals who have explained the correct process. Patterns can be used to evaluate your equipment (gun, choke, and loads) as well as yourself (aim, grip, etc). To separate these variables, you should evaluate your equipment, so you can better understand that you are not incorrectly adjusting before you evaluate yourself.
To properly pattern a shotgun, you need to first decide your goal. The common standard to identify a choke performance is the number of pellets in a 30 inch circle at 40 yards. However many individuals like to evaluate the pattern at the distance that they intend to shoot at. This is fine, just understand that tables identifying "effective choke" are based on the 40 yard standard.
Evaluating equipment is the most common reason for patterning. To properly test your gun, choke, and load combination, you first need to remove human factors from the test. Shots should be taken under the best gun rest conditions that can practically be provided. Though there are better ways, sand bags on windless days are pretty good. Shotgun patterns are very random. The Shotgun Analyzer program allows you to average as many targets as you care to shoot. The NRA recommends 10. Randy Wakeman for practical reasons likes 5. Target Telemetrics recommends that you shoot until you see a consistency that you trust while still enjoying the day. If you are using the iPhone app you should gauge your results by the shot with the most typical results. Always save your data somewhere, you may want to compare at a later time.
Your study goals will vary based on your sport, but there are some basics.
1. Point of impact - Windage, Elevation, Offset. There is not a lot you can do to correct a gun with a fixed choke that has a 10 inch windage other than getting a new gun(yes we see these). There are smiths who will bend a barrel and you can also adjust a back site. If you have an adjustable choke, you will likely find that the windage and elevation may change accordingly. If you have an adjustable choke, you probably already have some ideas about how you intend to use it.
2. Effective choke - The table below is a guide to cross-referencing a choke. Hopefully your choke complies. % efficiency is the base parameter used to determine choke and is used in conjunction.
a. Extra Full > 75%
b. Full > 65%
c. Improved Modified > 55%
d. Modified > 45%
e. Improved Cylinder > 35%
f. Skeet > 25%
g, Cylinder > 15%
3. Averaging - Before you make any expensive assumptions, look at several patterns as well as the average to score a gun, choke, or load combination.
4. Comparisons – At this point many people will want to change shells or chokes and make some comparisons.
Once you have arrived at a gun, choke, and load that you are satisfied with you may want to evaluate yourself or a student. To do this you simply set up the performance conditions. Standing, 2 targets side by side for multi-shot, etc. Performance is evaluated by the point of impact offset from the aim point. You may need to correct for the “known offset” as well. Success is the next test. This is a way of translating everything into a pass fail for the shot. To achieve this adjust the circle to include the aim point (whether it is the bullseye or the equipment offset. The density of this circle is your pass fail. This density is the density required to break a clay or kill a bird. See the kill ratio page for this table. Pass/Fail is also possible to do with smaller kill zone targets as well. Once you have confidence in your pattern, you will save money and time by using the smaller targets.