The following excerpt is pretty in depth and comprehensive but is packed with a lot of valuable information. Please take a moment and post your ideas and suggestions as well.

Full source with pics: http://njgunforums.com/forum/index.php? ... -be-lying/

How to Pattern Your Shotgun (and why your choke may be lying)

Patterning should be the first thing you do when you take possession of a new shotgun, however all too often I talk to people who don’t even have a clue what their shotgun has for a choke! Patterning is critical, because while your choke my say “modified” on it, how do you know it delivers “modified” performance as far as pattern density? The only way to find out is the pattern!

The first step to patterning is to grab yourself some big paper. 40x40 inch is the recommended, but I grab old drawings from work which are 36x48” and work just fine. A freestanding patterning board is ideal, but even an old pallet propped up with a stick makes a great holder for this size paper, too. The dimension of the paper isn’t terribly critical, however what IS critical is your distance from shotgun to paper. Shotgun patterns widen the further out you go, therefore if your choke should deliver 70% pattern density at 40 yards, it will pattern looser if you throw the board up at say…50 yards. This will skew your results. Get yourself a BIG tape measure and measure out 40 yards. The more exact you can do this the truer your results will be!

At the range

Now we get to start shooting stuff! Ideally, you will pattern every load you may want to use, out of every shotgun, out of every choke. This can be a daunting task, because if you have 4 chokes and 4 different types of ammunition to pattern, that’s a whopping 16 different combinations to try. I recommend you shoot 3-5 patterns with each combination so you get an accurate representation. So you are looking at 48-80 sheets. This is not a process for the faint of heart. Set up your target at 40 yards and draw a POA (Point of aim) that is in the center of the target and just large enough to aim at. Put your shotgun on a rest (yes, bench resting your shotgun!) and carefully fire ONE round directly at your POA. Now, write something on the top of your target so you know which way is up, and write on the target what shotgun, choke, and load was fired at it before you forget. Repeat as necessary!

Understanding the data

OK, so now you are home, exhausted, and have a massive pile of huge targets with tons of little holes in them. Now what? Well, now comes the fun part.You need to create a 30” circle around the densest portion of your pattern. NOT around your point of aim, but around what you feel is the center of your pattern. You can do this one of two ways. First way is cut out a 30” circle of cardboard with a hole in the middle. Put it over where you want, mark the center (important) and trace it. The other option is use a 15” string and pencil. Either way, make sure that you mark your center for the next step. Now you quarter your 30” circle. Just draw a horizontal and vertical line to divide it up into 4 sections. Following that, count all the holes in each quarter and white the number down on the paper. It helps to tick off the holes as you go. Now you take those 4 numbers and add them together, and put them with your notes on the side. This is your total pellet count.

Now you are ready to finally evaluate your pattern. First and foremost, just looking at it you want to see an even distribution of numbers across the 4 quarters. In a perfect world, you want 4 of the same numbers which would mean you pattern is evenly distributed…perfectly. Also, you want to look at how your pattern is aligned with your POA. For a field gun you want your POA to be the same as your POI (point of impact). Lots of trap shooters like to have a 60/40 pattern for rising shots which would mean that 60 percent of the pattern is in the top 2 quarters and 40 percent is in the bottom two. Evaluate your pattern accordingly. You also want to look for any big gaps in the pattern that would allow a target to fly through. The final step is calculating pattern density. This is how you ascertain what choke your load/choke/ shotgun combo is actually shooting. To determine pattern density you divide the total amount of holes in your 30” circle by the total amount of pellets in the loaded shell Here is a table showing the pellets/oz.

Shot#, Pellet Diameter (Inches), Average Pellet Weight (Grains), Approximate # of Pellets per Ounce
12 .05 .18 2385
11 .06 .25 1750
9 .08 .75 585
8 1/2 .085 .88 485
8 .09 1.07 410
7 1/2 .095 1.25 350
6 .11 1.95 225
5 .12 2.58 170
4 .13 3.24 135
2 .15 4.86 90
BB .18 8.75 50

And with that, you can then get your percentage and see what choke your gun is actually shooting at. This is all assuming testing at 40 yards.

Cylinder %40
Skeet 1 %45
Improved Cylinder %50
Light mod %55
Modified %60
Improved Modified %65
Full %70
Extra Full %73
Turkey %75 plus

So there you have it!

Don't be surprised if your “modified” choke actually shoots like a skeet choke, or even a full choke. Anything is possible! This is why patterning a shotgun is essential. If your modified choke performs like a full choke, you do not need to put a full choke on for those further out shots as you will be over choking your shotgun.

Decent pattern. Note the top is marked, and the circle is centered on the most dense portion of the pattern. The big black criss-crossed circle was my aiming point.This pattern shows that the shotgun patterned slightly low on this particular shot but has decent distribution.This comes out to 73% which is extra full performance that shot out of a tube with "modified" restriction.There are some undesirable voids.

Here is a pretty lopsided pattern out of my Mossberg 20ga. Notice the very uneven distribution and how it is somewhat off center.

This is a gorgeous pattern! It is off the POA but this can be due to thing like wind, poor aim, or just poor judgment when making the circle. Note the vey even pattern with no voids. This pattern is 56%, out of a "modified" choke so it actually fell 4% short of what it should pattern at.

You can even go so far as to create a spreadsheet to compare loads. Below is a sample of mine. For the 20GA loads at the bottom you will notice notes such as “Full +1”. This is because that particular shotgun had a c-let adjustable choke and I was experimenting with cranking it tighter than full to see if I could get it to choke down more, because of the previous poor patterns. This is a GREAT example of why to pattern, because after this I would NEVER rely on this shotgun to take long shots.

Why patterns matter

Finally, a brief note on choke tube selection. I prefer the extended choke tubes, and this is for three reasons. My primary reason is ease of changing. If you ever shoot sporting clays and want to take it seriously, you will most likely find yourself changing chokes every now and then. With an extended tubes, you do not need a wrench because you can just grab it and twist it out since it extends out the muzzle. The second reason is ease of identification. It is easy to lose track of which choke is in your shotgun, and most extended tubes are clearly marked on the extended portion. The third reason is pattern quality. Since the constriction takes place over a longer distance it is less likely to deform your shot and degrade your pattern. Once you have patterened your shotgun and are intimatly familiar with your shotgun, you will find yourself changing your chokes all the time for different shooting distances/styles for maximum advantage. This is when you will really want to have the extended tubes for ease of changing, and while your at it, pick yourself up a nice choke tube case to keep them in.

If your pattern is less than perfect

Now, what do you do if your results are not acceptable to you? If your patterns have voids or are uneven, it can be a factor of the shotguns barrel, the choke, or the ammunition. To determine which it is, simply utilize process of elimination. Try your choke in another shotgun which has an established performance. If the other shotgun patterns poorly with your choke, then your choke is the issue. If it patterns fine with your choke, go ahead and try your ammo in that shotgun. Again, if that yields poor performance, the ammunition is your problem. If that patterns fine, it is a safe bet that there is something wrong with your barrel that is contributing to poor patterns, such as a poorly done back-boring, the forcing cones are messed up, excessive fouling etc. However if your issue is a point of impact that is very far off of your point of aim, your best fix is to sell the gun. There are a few fixes but all are complex and beyond the ability of a tinkerer. A non ribbed barrel can be bent, but I would leave this to a professional. You can also get Briley to cut you an eccentric choke, which is another expensive proposition and it would have to be carefully indexed every time you put it on. As I said before, your best bet here is to sell the shotgun and obtain something with better performance.

Extended choke tubes, tube cases, wrenches, and a refrence chart from the choke manufacturer stating theoretical pattern densities.

The ultimate in being prepared is having an over/under style shotgun where you can have two different chokes on the gun at the same time, and being able to select which barrel fires first! This is especially advantous if you are doing doubles at a sporting clay course. For example, say you have a report pair. This means that once you fire your first shot, a second clay is thrown. Lets say you have a pump action 870 and a wide assortment of chokes. The first clay is a crossing shot, very close and right ahead of you. The second clay is thown from 20 yards ahead, and goes away from you. You can only select one choke. Which do you chose? If you chose a cylinder choke you will be best prepared for the first clay, however the second clay will be nearly impossible. If you chose a full choke you will have a very difficult time hitting the first clay, but it lets you reach out to the second clay. A modified choke will make each possible, but both would be moderatly difficult. Having an over/under allows you to put on a cylinder and full choke at the same time, and then you can chose to fire the cylinder choke first. This way, your close shot you pull the trigger and the barrel with the cyl choke lets loose on the first clay, and then you fire the barrel with the full choke at the distant clay. Knowing your shotgun and your chokes is important so that you can get the most from your equiptment.

Very sage advice. You wouldn't take a new scope and go hunting without sighting it in, why would you take a shotgun out and not pattern it?

I like the extended choke tubes, too, but for the reverse reason. If you do alot of shooting they can get a little loose. Extended tubes make it easy to tighten them back up!

Welcome to the Ithaca Owners Forum as a moderator Simpleman !!

...very good post also !

+1 rep to put you on the board

We patterned our muzzle loading shotguns, and found amazing differences between BRANDS of BP. One brand (same granulation, same charge wt.) gave a really tight, even pattern, while another gave patterns with holes so big that you could throw a cat through them.
To a reloader, if you are changing components in a load, you need to pattern it again.

You make a very valid point, BP. The reason for this is related to my earlier post. One brand might have the same shot size, velocity, etc, etc but the internal pressure of the powder charge, the wad and the hardness of the shot all play a very important role in how a gun will pattern. also add to this the angle and length of the forcing cone, the choke type, the bore (backboring, etc) and even the length of the choke it is amazing we can even hit a barn door much less a rabbit or a clay.

SHOOTER13 wrote:Welcome to the Ithaca Owners Forum as a moderator Simpleman !!

...very good post also !

+1 rep to put you on the board

Thanks!

+1. I have fixed choke guns that if you shoot one brand of shells in tend to pattern one choke more open, and with another major brand shoot what they are marked. I'd have never known if I didn't pattern.

Its pretty amazing when you start patterning a gun and you realize that theres such A big difference among brands, shot weight, shot size, and powder charge. I have a Stoeger sxs that is choked ic & mod but is closer to mod & imp mod with nearly anything except Remy express long range 1 1/4oz loads and then its about right.

I also own a Stoeger sxs...the Uplander. My very first shotgun...

I don't know if this holds true across the board for all folks, but it has been my experience that in my guns Federals tend to pattern tighter than Remingtons. Now it shouldn't surprise me that they pattern differently, as they use different constructions, wads, and other components. But as far as I can remember out of the guns that I have patterned this has held true every time. YMMV.