I like your idea that at any given range, 77% is the optimum pattern density. But that is for 12 gauge. I am a skeet shooter, and would like a nice rule of thumb that would work for other gauges too. I have given some thought as to how one could deduce a similar rule of thumb for the other gauges. I don’t think pro-rating the percentage would be useful, nor would changing the distance. Sooooo….I’m guessing that perhaps it would make sense to pro-rate the size of the pattern. I’ve attached a worksheet for your consideration, comments, and critique. 706.5 Sq Inches in 30″ circle
Gauge Ounce of Shot Pro Ration Sq Inches in Pattern Diameter of Pattern
12 1.125 100.00% 706.5 30″
20 0.875 77.78% 549.5 26.5″
28 0.75 66.67% 471.0 24.5″
410 0.5 44.44% 314.0 20″
So, for the .410; 77% in a 20″ circle at 21 yards would be an optimum
pattern for say station 4 skeet. Make sense?
I shoot a bunch of skeet also, so I’m as interested in this stuff as anyone. I’ll tell you right up front that you are going to have to do a bunch of patterning. I can give you the “computed” ivory tower numbers to look for, but you are going to have to do the grunt work to find out exactly what constriction of choke gives you what you need.
I don’t think that “pro-rating” is quite the way to go here. Let me do it another way.
First of all, I’m going to suppose the use of #9 shot using the standard pellet count 585 #9s per ounce.
The formulae I use comes from Ed Lowry’s “Shotshell Ballistics for Windows”. Lowry uses a Gaussian distribution to predict patterns within a 30″ circle. Everything is based on the percentage of strikes within a 30″ circle. Once you know the percentage of hits in the circle, you can calculate the percentage probability of a certain number of hits anywhere within the circle.
I like Warren Johnson’s “Choke Chooser” criterion of a killing pattern being a minimum of a 95% chance of a one pellet strike (statistically equal to an 80% chance of a two pellet strike). That’s what I factor into the Lowry formula.
I also use 6 square inches as the target. That’s the area of an edge-on standard clay and is typical of skeet crossers at 3,4 and 5.
So, here are the numbers generated. Remember, they represent the diameter of a killing pattern given the percentage of #9s in a 30″ circle which, in our case, is placed at 21 yards. The percentages would be the same where ever the 30″ circle were placed, but obviously the choke required to produce them and the pellet size need for adequate pellet energy would change if distance increased.
7/8 oz, 512 count #9
70% pattern equals a 20″ killing circle
3/4 oz, 439 count #9
70% pattern equals a 17″ killing circle
1/2 oz, 292 count #9
70% pattern equals a 5″ killing circle
So, if you want the best chance of killing that skeet target you will choke your 20 gauge to produce 80%~90% patterns in a 30″ circle at 21 yards. Your 28 will give you the best chance at 80%~95% and the miserable little 410 will make you a hero if you choke for 90%~99%.
It will be up to you to decide how much choke constriction it will take to produce these pattern percentages in a 30″ circle at 21 yards. That means time spent at the pattern board with a pocket full of screw chokes or different reloading recipes. I never said it was easy. At least each gauge gives you an optimum range.
Warning: expect patterns from a single choke and a single shell to vary at least 10% shot to shot. That’s the nature of shotgunning. It’s a random event that only evens out after a considerable number of iterations. One pattern doesn’t tell you much. Five is better. Ten is quite good. Let’s see: ten patterns per combination, perhaps 5 combinations, three gauges. Do you have a life?
Also, you should bear in mind the criteria I use. You may or may not be satisfied with a 95% chance of a one pellet strike as defining your outer fringe. You may prefer #8-1/2s to #9s, in which case you will lose pellet count, but gain energy. You may not choose to choke for 21 yards.
Ed Scherer once told me, when I asked him how to choke a tube set, that .007″ in all three subgauges wasn’t a bad way to go. Personally, I like a bit more in the .410, say .010″, but I didn’t argue with a man with that much experience.
I don’t know if you would be better served spending all your spare time experimenting with chokes or spending the same amount of time and money actually practicing the game. One thing is for sure. As the shot charge does down, the choke goes up. But you knew that.
The Technoid writing for Shotgun Report, LLC
(Often in error. Never in doubt.)