After doing a thorough pattern test and analysis it’s time to focus on how to increase pattern density and consistency, as both are needed for a complete shotgun pattern tuning. There is some knowledge worth having first as to what you are dealing with.
A True Shot Pattern Is, 100% Of The Shot In A 40 Inch Circle:
- Full choke delivers a 40 inch 100% pattern at 40 yards.
- Modified choke delivers a 40 inch 100% pattern at 35 yards.
- Improved cylinder choke delivers a 40 inch 100% pattern at 30 yards.
- Cylinder bore delivers a 40 inch 100% pattern at 25 yards.
A Good Pattern Is, 70% Of The Shot Within A 30 Inch Circle:
- Full choke delivers a 30 inch, 70% pattern at 40 yards.
- Modified choke delivers a 30 inch, 70% pattern at 35 yards.
- Improved cylinder choke delivers a 30 inch, 70% pattern at 30 yards.
- Cylinder bore delivers a 30 inch, 70% pattern at 25 yards.
Determining Pattern Density:
To determine pattern density you first have to understand it. When we pattern our shotguns we try to make good use of the shot in the shotshell but right from the beginning we give up 30 percent of what’s available in the shotshell, as we are looking for 70 percent patterns at various yardages, this obvious loss is do to lack of pattern density.
In a 40 inch diameter circle there are 1,256.63 square inches. In a 30 inch diameter circle there are 706.85 square inches of area that needs filled evenly with a small amount of shot, by breaking this area down into 2 even areas we find that inside that 30 inch diameter circle is another circle that is 21.21 inches in diameter both having equal area at 353.425 square inches each.
Below is an image of what an actual shot pattern is, containing 100% of the shot in a shotshell and yes that was done to scale. That image reflects for the most part a complete full choke shot pattern at forty yards, total shot spread of 40 inches. 30% of the shot will be contained in the darker outer ring that has 549.78 square inches of space that gets dis-regarded when patterning. 70% of the shot will be contained in the two inner lighter gray areas that has 706.85 square inches of space.
When trying to increase pattern density we are trying to bring that lost 30% of shot in from that outer 40 inch ring and bring it closer to the inner 30 inch diameter circle and make use of that in a better shot pattern. The other side of this scenario is we are trying to even out the pattern so as not to have holes that targets can slip through.
The one thing you have to understand is, why is it that 30% of the shot that should be in the usable pattern isn’t. The reason for this is simple, for the most part, lead pellets crush and deform quite easily, dented and deformed pellets wander out of the shot column fairly easy as they push through the air. Round pellets or undamaged pellets tend to stay the general course to the intended target.
Pattern Density Improvements:
1. In a first attempt to increase the pattern above 70%, could be something as simple as shooting a lower velocity load with the same size and weight of shot as previously attempted. A lower velocity load will exert less force on the shot column and therefore not deform or dent as many pellets as before thus increasing pattern density.
2. In a second attempt for better patterns this one is very common, check the bore of your shotgun. Shotgun bores foul with powder and plastic residue more than you think and will absolutely destroy shot patterns and change point of impact. If this is the case for you, there is a way to slow the fouling process considerably and that is done by bore burnishing. This process is simple and quite easy. This makes the bore area of the barrel very slick so as not to drag and destroy the purpose of plastic wads, it also resists powder residue fouling.
3. In a third attempt to improve shot patterns, another thing to consider if this is a shotgun you recently purchased used, it is worth noting one characteristic of this shotgun besides needing help with the pattern. Does it seem to recoil more than you think it should? If this is the case you may want to check the length of the shotshell chamber area as many older shotguns will have short chambers. Any competent gunsmith can remedy this and give you a pattern increasing, recoil reducing, longer forcing cone all at the same time. This is very beneficial.
4. In a forth attempt to increase shot count in your pattern, after you analyzed your shot pattern with a Lockhart Pattern Gauge you noted that there was a consistent hole in your pattern. I designed those gauges just for the purpose of finding bore defects, so you look in the bore and there it is, a rust cavity. A little back-bore work is needed here, again most competent gunsmiths will make a clean up pass with a slightly larger combination bore and choke reamer to fix this problem and it does nothing to reduce the velocity of shotshells.