Shotgun-Insight Pattern Optimiser (Why & how to use it!)

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(c) Written by A C Jones


Why use the Pattern Optimiser?

This Pattern Optimiser and the Shotgun-Insight pattern measuring software work together. The pattern measuring tells you what spread you have. The Pattern Optimiser helps to determine if this can be improved for the distance and discipline being shot.

The Spread Optimiser can:
Estimate the skill of the shooter! Show the effect of altering the spread. Show the effect of POI offset errors. Show that multiple pellet strikes are not needed to break a clay.
Example: Estimating the skill of the shooter and optimising the pattern spread.



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In Trapshooting the target break distance is relatively repeatable. To get "good" a shooter is also probably pretty repeatable. That is the placing of the shot on the target is relatively predictable shot to shot, day to day. The difference between a "good" and an "excellent" shooter is the amount of variation they exhibit in the shot placement shot to shot. That might sound obvious, but if one considers Sporting Clays, sometimes a score will be way above or below the long term average simply because the shooter couldn't figure out some presentations on a particular course. A low score isn't due to poor gun control, it's due to not even being close to reading the line of the clay. Similarly with Skeet, the average score is probably determined by a few bogey stands rather than an even rate of missing around the whole layout (H2, L6 spring to mind along with the pair on stand 4 in English Skeet. The rest are normally considered straight-forward). So, for a Trap shooter, the long term average is a good indication of how variable the shooter is in placing the centre of the pattern on the target.

If the the pattern spread (either the 75% spread figure from Shotgun-Insight or the traditional pattern efficiency) of the gun and shell combination is known at the break distance, then this combined with the shooters average can be used to estimate just how much variation the shooter exhibits when placing the shot. Here are the steps to estimate this shooter shot to shot variation:

Set the known pellet count.
Set the typical target size. For Trap this is normally a "trap view" which is approximately 5sq inches. Quick shooters will see a little more target, slower shooters or those who shoot in cross wind conditions might tend to get flatter presentations. Whatever the real view, subtract a small amount. This is to remove the outer edges of the clay from the analysis where a pellet strike might glance off the clay or chip the clay by such a small amount it is not called as a kill. By considering a slightly smaller target size any pellet strikes on the target can be considered solid ones and hence break the clay. This makes the hit probability figures of the Spread Optimiser easier to follow. Just consider the 1+ pellet strike figures and graphs knowing that one or more strikes will break the clay.
Set the 75% spread diameter slider to the known pattern width or to show the known pattern efficiency. Unless the pattern is very tight, most likely the pattern (even at the centre) does not give 100% chance of a pellet strike. If necessary zoom the graph to see what is going on at the centre of the pattern. Even if the chance of a pellet strike is near 100% in the centre the probability drops off quickly. It is the complex nature of this reduction in the likelihood of a pellet striking the clay that makes estimating the effectiveness of patterns so difficult. The Spread Optimiser helps by giving an average of the hit probability figures over the range of distances from the centre of the pattern to the worst case limit of the shooter's ability to place the shot.
Adjust the Shooter Skill Slider until the Overall Chance of 1+ Pellet Strikes matches the average score. The Shooter Skill Slider now shows the precision of the shooter!
It gets better . . . . Now go back to the 75% Spread Diameter slider and adjust it up (and down) to see if the "Overall Chance of 1+ Pellet Strikes" can be increased appreciably. If it can, then the pattern spread should be tightened (or opened) to help increase the scores. Generally a tighter choke favours a better shooter. As the skill level and averages improve there may come a time when it makes sense to tighten up the choke to match this improved skill level.


Example: Show the effect of a gun horizontal POI error. (NB this feature benefits from a fast computer)

Some shotguns don't shoot exactly to the horizontal point of aim and barrel convergence is also often not perfect. There are occasional stories of horror guns that point a foot or more away from the point of aim. At what point should a shooter worry about the distance between point of impact and point of aim and barrel convergence? 

The effect of a fixed gun error depends on the tightness of the pattern and the skill of the shooter. Good shooters will tend to use tighter choke. The combination of a shooter who tends to centre his shots using a tight patterning gun makes the effect of gun errors more significant. As an extreme example the pictures below show a very tight pattern with a full 8" of POI error. 

The white ring shows the area into which the shooter places 95% of his shots, i.e. the skill level of the shooter. In this case perfect shot placement on the part of the shooter would result in a miss. Of course it is quite possible that a shooter would subconsciously learn to give more lead on right to left crossers than on left to right crossers (though top and bottom and barrels pointing in different directions would be difficult even for the best shot!). On average it must surely be better to get the gun "about right". How "right" is "about right"? The effect of point of impact offset on the chance of hitting the target can be estimated by adjusting the Offset slider. First, set the user skill level, pattern spread, pellet count and target size. Then look at the "Centre weight 1+ pellet strike" figure as the Offset slider is adjusted.

For typical clay loads and target sizes a 2" offset reduces the chance of hitting the clay by ~0.7%. A 4" offset causes the chance of hitting the clay to reduce by approximately 2%. 

Getting the POI right is probably something worth investing in and something that a good gunsmith or stocker should be able to carry out. Interestingly, if one does want to get the POI to less than approximately 2", the normal advice of patterning at a short distance (say 12 yards) is probably as much a hindrance as a help. At 12yds the POI must be judged to approximately 0.6" in order to determine that the 40yd POI is less than approximately 2". Judging the POI by patterning at 40yds either needs a rest and averaging a good number of targets, or alternatively, mounting and shooting at the pattern plate as though shooting a going away clay and averaging an even higher number of targets. Judging the POI is going to be hard work no matter how the testing is done. However, it could help deliver a clay or two to the long term average score.

Example: Number of pellets needed to break a clay.

It is a commonly held belief that it takes "at least 5 pellets to reliably break a clay". The Spread Optimiser can help show this isn't the case. Setting a pattern efficiency of 75% with a 600 pellet count and an edge on target size of 4.2" represents a typical 1oz No9 skeet load and an edge on target taken near the centre peg on a skeet layout. Switching on the 4+, 5+ and 6+ pellet strike plots gives the graph shown below. 

Graph showing the probability of 1+, 2+ up to 6+ pellets striking an edge on clay when a 600-pellet shell is used.

The yellow line highlights the curve representing the probability of one or more pellet strikes on the clay and how this varies with distance from the centre of the pattern. It can be seen that this 1+ pellet strike curve peaks at about 99% in the centre of the pattern.

The red line highlights the curve representing the probability of five or more pellet strikes on the clay. This red line peaks at ~56%, i.e. if five or more pellets were needed to break a clay, in this example the clay would break on average 56% of the time even if the shooter centred every shot perfectly.

Common experience demonstrates that a 600-pellet skeet load whatever choke is used gives way more than 56% of clays broken at skeet ranges. 

Does 5+ pellet strikes give a better break? Yes. 

Are they needed? No. 

Is one pellet a enough? Most of the time. Clays are not of uniform construction. It is quite possible that sometimes a pellet hits the clay and it does not break. But the statistics suggest that most of the time they do.




 (c) Dr A C Jones      June 2005