How do I pattern my new shotgun to determine where it is shooting?
I get asked this question at least twice a week so I thought I would share the answer here.
Above Photo: Bottom Barrel: 20 metres - Modified Choke - 55%/45% pattern - Shotshell: RC 4 24g 8 1/2
Above Photo: Top Barrel: 20 metres - Full Choke ( after the stock was raised 4mm ) 70%/30% pattern - Shotshell: RC 4 24g 7 1/2
Ideally find a steel plated pattern board that is at least 125 cm by 125 cm in size and is supported at around 100 cm above ground level at the base of the board. Mark a clearly visible 3 cm spot in the middle of the board. A great mixture to paint the board with is 1/3 motor oil and 2/3 white oil based paint. If this isn't available then a runny paste of water and builders lime is sufficient. Please wear safety glasses when testing a gun against a steel pattern board especially when using steel shot as ricochets can occur. Using butchers paper over the top of a board is yesterday's news. It is far easier to take a photo of your pattern with your mobile phone and it is stored forever. Email to yourself and you can even get it printed out on an A4 sheet of paper to show a hard copy to your local gunsmith.
If you are simply wanting to check where your shotgun is shooting then stand no further back than 20 paces (20 metres maximum). Fire a shot at the board ONLY once you are comfortable with your gun mount and are confident you are mounting the gun in the same manner that you would be on the range or in the field. Aim at the board like you are holding a rifle. By this I mean concentrate on seeing the end of the barrel clearly and the mark in the middle of the pattern board as a blur (it is the only time in shotgun shooting I would ever ask anyone to do this). Concentrate on squeezing the trigger slowly like a rifle and not jerking it. If you pull the trigger in a harsh manner then the pattern will have a tendency to shoot artificially to the right if you are a right handed shooter.
If you are happy with the first shot then take careful note of what percentage of the pellets are above/below or left/right of the aiming point. Wipe the board and repeat the process, but this time fire three shots (with the bottom barrel only) before walking forward and taking note of the percentages. By firing three shots you will get a very clear picture of your shotguns hitting point. If you have a camera/phone take a photo of this pattern on the board before you do anything else. You will need to refer to this pattern after you have made any changes to your stock and/or technique. If you have an adjustable stock then make the required adjustments. Drop the comb to lower the pattern, lift it to raise the pattern. Move the comb right if it shoots left and vica versa if it shoots right. 1mm adjustment will only alter the pattern 4%. If a gun is shooting massive amounts off centre then a technical change may be required OR a trip to a qualified gunsmith to see if your barrels are in fact out of line.
To test your top barrel ( second shot ) load both barrels and repeat the process BUT fire the first barrel slightly off to the right OR left of the pattern board and WITHOUT MAKING ANY HEAD ADJUSTMENT ON YOUR STOCK swing back to the centre of the board and when the shotgun stops moving repeat the procedure as per the first barrel. Again see the front sight clear and the centre aiming point of the board as a blur, but do not make any realignment of your head/eye down the centre of the barrel. This will give you the information that you need to determine if your pitch, cast, or the drop in the comb need adjusting. The second shot needs to be tested in this manner to determine if the recoil of the first shot is affecting your eye alignment down the centre of the barrel. Any or all of the previous factors may need changing if the recoil of the first shot is upsetting your head/eye to barrel alignment.
If you notice the shotgun bouncing upwards after you fire the first shot then you may need to add pitch (increased angle to the butt of the stock) and the opposite if the barrels are being pushed down. If the pressure of the stock is increased on your face after the first shot thus causing you to look down the left side of the barrel slightly (assuming you are right handed) then you may need to add cast (move the comb to the right) or sand some wood off. If you tend to look down the right hand side after the first shot then the comb may need to be moved to the left or some tape added to the left side of the stock if your stock is not adjustable. If you feel a significant amount of recoil to your face then the angle of downward "drop" in the comb may be too great and should be lessened.
Both the top and the bottom barrel should shoot in the same place.
If you are patterning to check percentages of chokes or shot shell performance then a more specific distance will be required. At greater distances the aid of a support of some description may be desirable, but to simply find where your shotgun is shooting then freestanding at a maximum of 20 metres is sufficient. Remember it is only a percentage above and below or left and right of centre that you are looking for. Twenty metres will allow even the tightest of chokes to open the shot pattern up enough to make this assessment. If you stand to far from the board then human error becomes a far greater variable when trying to hold the shotgun steady and aim. Shotgun shooters generally are not the greatest at holding a gun steady for any length of time.
The shot pattern used in the above photos was from an Olympic Trap shotgun I tested at Tucson, Arizona earlier this year. I had a suspicion that the firearm was shooting quite low and sure enough the pattern testing proved my assumption. 4mm added to the combs height raised its pattern percentage from 55% high to 70% high. It is irrelevant for pattern testing what distance the shotgun is tested at if it is done correctly. The pattern percentage will remain constant whatever the distance. It is only the width of the shot dispersion that will vary.
As a rough guide these are the types of patterns you are looking for for each discipline of shotgun shooting;
Field: 50% above and 50 % below the aiming point. (this is the lowest you would ever want a shotgun to shoot)
Sporting Clays/ Skeet: 60% / 40% (+/- 10%)
Olympic Trap: 65% / 35% (+/- 10%)
DTL (American Trap): 70% / 30% (+/- 10%)
Double Trap: 80% / 20% (+/- 10%)
Remember the pattern board is not your wife. It will never lie to you. If done correctly it is a hard copy blueprint of your sight picture. I am amazed how many shotgun shooters have no clue where their firearm really shoots. Most are guessing and these are really the dumb shooters. You always sight in a rifle so why not your shotgun? For the sake of a handful of shot shells you may save yourself thousands of dollars.
Happy to answer any questions you may have on this topic.
I hope this helps. Good luck in your shooting.