Shotgun patterns made simple - all you need to know in one page!
As a shooter there are only two things you need to know about this bell-shaped pattern:
That's all there is to it! Determine the pattern width you need, then find the shell that does it best every time. Easy!
Shotgun-Insight helps you by:
Most shells measured will appear to follow the "bell-shaped" distribution closely. However, the pellet distributions are actually a "sum of bell shaped distributions". Each component of the shell - the crimp, powder, primer, pellets, and temperature etc will be subject to shell to shell variations and contribute to the overall shot to shot variation. This is a fact of any manufacturing process or manufactured product.
Some shells behave very differently with temperature variations. You should either pattern at different temperatures and understand how the spread varies, or, use a shell that is affected less by temperature variation.
In practice it is the inherent variation of the cloud of shot that dominates the spread. This is what gives the spread we expect of a shotgun and it is this spread of shot that on average follows the bell shaped distribution.
However, there is a subtlety even to this that may be very pertinent to shotgun shells. Imagine a shell with a very long shot column: Pellets at the top of the column will have one set of pellet to pellet variations causing them to spread following a certain bell-shaped distribution; Pellets at the bottom of the column may get much more deformed to the extent that they follow a different distribution, i.e. a wider spread than those at the top of the column. Careful analysis of ratios of pellet counts between the outer and inner regions of a pattern and between different shells or forcing cones will quantify the effect of pellet deformation at the base of the shot column. To date I have not found any consistent difference between 24g and 28g shells with their different shot column heights, at least not from testing at 25yds. Long range (40yds) testing will take place in due course.
People often talk of 'even' pellet coverage. Shotgun patterns are not even, they are bell-shaped! And this is helpful because:
(c) Dr A C Jones