Point Of Impact
Contents of this page
The simple definition is:
The point where the centre of your shot string is in relation to your aim point at a specified distance.
Here is an example
This shows a 30" diameter circle enclosing 90% of the pellets that hit a pattern plate at 35 yards. (The orange shapes represent the size of a standard clay shown face-on and edge-on at the correct scale in relation to the size of the circle.)
The shooter's point of aim is indicated by the yellow front bead above the black barrel.
In this case 70% of the pellets in the circle fall above the point of aim and 30% below it. This is often described as a POI of 70/30.
Since we know that the circle is 30" in diameter we know that 21" (70%) of the circle is above the point of aim and 9" (30%) is below it. The actual centre of the circle is 6" above the point of aim. This is an alternative way of specifying POI.
So, assuming a 30" circle, a POI of 70/30 means that the centre of the shot string is 6" above the point of aim at 35 yards.
Another example
In this example the POI is the same as the point of aim. In other words, this barrel is placing the centre of the shot string at the point of aim at 35 yards. 50% of the pellets are above the point of aim and 50% below it - a POI of 50/50.
Trap guns tend to have a higher POI than Skeet or Sporting guns. This is simply because a trap clay is normally taken when it is rising so placing the majority of the pellets above the point of aim will tend to catch the clay as it rises between the time the trigger is pressed and the time the pellets reach it. The method used by the manufacturer to set the POI is normally to alter the rib but a similar effect can be obtained by a modified comb.
Shooting trap with a sporting gun can put you at a severe disadvantage because the only way you are going to place the pellets high is to raise your point of aim until it covers the clay. Shooting at a target you cannot see is possible but it is certainly not ideal.
ATA trap guns
Most shotguns used in American Trap Association (ATA) competitions have fairly high POI values.
Some specialist shotguns used for ATA doubles competitions have different POI values for each barrel. the first barrel may be 70/30 (placing 70% of the lellets above the point of aim) but the second barrel may be 100/0 - placing 100% of the pellets above the point of aim because the second clay in doubles will be further away than the first.
POI values expressed as two percentages tend to run out of steam at 100/0 but some shooters have guns which fire much higher than this. A 100/0 POI within a 30" circle will be putting the centre of the shot string 15" above the point of aim. Some shooters have the second barrel placing the centre of the shot string 22" above the point of aim!
Every shooter should check the real POI of his shotgun - the POI of each barrel in the case of O/U and S/S guns.
The procedure is very simple:
- If the club does not have a pattern plate it should build one - it is an essential item of club equipment. It needs to be about 6 feet square with its centre at eye height and built against a suitable backstop (a natural hill or a mound of earth) for safety reasons. Some pattern plates are made of sheet steel but there is the danger of ricochets - especially when using steel shot. A steel plate covered with timber (thin MDF is fine) is ideal because the timber can be changed after extensive use. A bucket of whitewash needs to be available close to the pattern plate so previous shots can be quickly painted over.
- Whitewash the club pattern plate so you can see your pellets when you shoot.
- Decide on the distance suitable for your discipline - maybe 35 yards for Trap or 20 yards for Skeet.
- Have a method of drawing a standard circle - a 30" diameter circle is ideal and a nail, piece of string and pencil will do the job!
- Paint a small visible mark in the centre of the pattern plate (or about 1/3 of the way up from the bottom if you know your gun shoots very high.)
- Stand at the required distance from the pattern plate, aim directly at the dot and fire. (Obviously you must be using your normal choke/cartridge combination.)
- Identify the centre of the shot patter by eye and draw your 30" dameter circle. The vertical distance from the aiming mark to the centre of your shot string is your POI expressed in inches. If the centre of the shot string is to the left/right of the aiming mark then you have a problem with your sight picture or you are canting the shotgun when you fire.
- Count the pellets within the circle and above/below the aiming mark and work out the percentage above and below. This gives you the POI expressed as two percentages.
- Repeat for the second barrel in the case of O/U and S/S shotguns.
Totally.
DryFire allows you to specify all the values relevant to each barrel of your shotgun. You specify the details of the cartridge (load, pellet size, muzzle velocity), choke used and POI value.
In this example the values for the two barrels are totally different - including different cartridges in each barrel!
Barrel 1
- Quarter choke
- Muzzle velocity 380mps
- Shot weight (load) 24g
- Shot size (No) 7 1/2
- POI measured at 32 metres
- POI pattern diameter 0.76m (about 30")
- POI: 50% above point of aim
- POI: 0m above point of aim
Barrel 2
- Half choke
- Muzzle velocity 420mps (higher velocity to chase that longer second target)
- Shot weight (load) 28g (increased load for longer distances)
- Shot size (No) 6 (increased shot size for more energy at longer distances)
- POI measured at 32 metres
- POI pattern diameter 0.76m (about 30")
- POI: 116% above point of aim (the aim point is below the bottom of the circle)
- POI: 0.5m above point of aim
Warning
Different cartridges in each barrel may get you thrown out of competitions!
Storing your most frequently used settings
You can change these settings as often as you wish and you can immediately see the effects thay have by looking at the on-screen results of each shot you take.
You can store different settings for different gun/cartridge/choke combinations ("Bob Smith (Skeet)", "Bob Smith (Trap)", "Bob Smith (Sporting)" etc.) so you are ready to practice with any combination simply by selecting a different shooter name.
Checking POI with the DryFire pattern plate
The procedure for checking POI using DryFire is as follows (numbers refer to the screen image below):
- Set up shooter, gun and barrel details as shown above.
- Select the Pattern plate option in the DryFire software.
- Use the Calibrate option to calibrate the DryFire gun assembly. Do this by shooting directly at the target spot in front of you. Note: it does not matter which barrel you have the muzzle insert in but it must be in the same barrel each time you use DryFire.
- Select the Shoot option (2).
- The program will select the 30m stand by default (1) but you can change it if you wish.
- Select the first barrel (3) and shoot again directly at the target spot.
- Select the second barrel (3) and shoot again directly at the target spot.
- Use the "8" key on the numeric keypad to zoom in for a closer look (4).
In this example we can see:
- The first shot is slightly lower than the aiming mark.
- The second shot is considerably higher than the aiming mark because the second barrel has a much larger POI.
- The second shot is slightly to the right - the shooter had probably been holding the gun in position for too long before firing.
We have received some correspondence raising some interesting point about POI so we have included it here for general information.
User comment: Currently we follow this process for each shooter:
- We first calibrate by having the bead of the gun just touching the bottom of the laser dot as directed.
- Next, we shoot at the patterning plate (30m) and, when aiming, we just cover the laser dot with our gun bead (as on the real patterning board).
DryFire comment: Minor point really: both the "Calibrate" and the "Shoot" shots in the Pattern Plate screen should have exactly the same point of aim. Personally I do both with the top of the front bead just touching the bottom of the target dot - like iron sights on a rifle.
User comment: Following the above procedure, if we have the percentage above the aiming point in the shooter's data set at zero as given in the directions for sporting guns, we are below the target on the patterning board.
DryFire comment: 50/50 is the normal POI. I.e. half the pellets above and half below the point of aim.
However, and this is a very big however, POI relates to a percentage at a specific distance. Obviously you could have 50/50 at 30m but the fall of pellets because of gravity would make this more like 20/80 at 50m (depending on cartridge etc.)
The default shot distance for the "Shoot" option in the pattern plate is 30m This should also be the distance you enter in the POI values if you want the shot to be in the right place at this distance.
User comment: If we set our sporting guns up at the 60/40 distribution we get on the real patterning board at our gun club, we also get the same result on DryFire's patterning board, that is, a 60/40 split. We understand from our shooting instructor that 60/40 is a common split for sporting guns.
DryFire comment: I agree with your instructor. There is no absolutely definitive setting because it varies depending on:
- Type of gun: sporting, skeet, trap.
- Manufacturer.
- Individual gun.
- Barrel - they may look parallel but that is no guarantee that they are! Some trap guns are specifically designed so that the second barrel shoots considerably higher than the first to provide the same sight picture for both clays in doubles.
If you wish to use POI properly you must use a real pattern plate to check your POI at a specific distance using a specific gun (and try both barrels) using specific chokes and specific cartridges. You will be surprised at the difference between guns - even ones that are supposed to be identical. That's why competitive trap shooters are so serious about checking real POI.
User comment: We would like to know why DryFire recommends using a zero pecentage above aiming point for sporting guns and also, would like to know how the new method differs from the old method (which seemed very accurate), that is, what was the split calculated under the old method?
DryFire comment: The "old method" (used in previous software) was the equivalent of 50/50.
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