First and foremost this is only a rough guide and the writer would advice each sportsman/ woman to have a guide/coach to help you to zero in your firearms.
This guide, mainly deals with rifles however the same principles apply to all types of firearms which need to be zeroed.
Also always keep in mind SAFETY and DANGER when handling firearms.
- When firearms are not in use i.e. when not on range the firearms must be kept unloaded; that is no bullet in the chamber and the magazine.
- The bolt/slide should be to the rear or removed.
- At no time should the barrel be pointed at any one.
- Never take it for granted that you have applied safety catch or that simply the use of a safety catch makes the weapon safe.
The perfect combination between rifle, ammunition and shooter, would be the ability to put every shot through the same hole at any range all the time.
But few things are perfect in this world, least of all arms & ammunition (sometimes the sportsperson).
It is important to understand the difference between consistency and accuracy and the factors that affect them.
Consistency is a measure of how close together a series of shots will fall to each other (group size).
Accuracy is how close a shot is likely to fall to the intended point on a target. This depends on a number of combination i.e. Group size, correct zeroing and the shooter's ability to select the correct point of aim to compensate for external variables such as range (distance) and wind.
If we say that all the external influences are minimal and the equipment and ammunition is of good quality, shots should consistently grouped within 1 minute of angle.
1 minute of angle measures approximately ½ inch at 50M and 1inch at 100 M and 2inch at 200 M. (more on this can be had on the net)
However the effect of many external variables increases with range and other factors, all this must be taken in to account.
External factors leading to inconsistency,
- Taking a slightly different aim for each shot- an imprecise aim will increase the size of the group.
- Variations in wind or other atmospheric effects between shots will increase of the size of the group.
- Poor shooting technique will send each bullet off on a slightly different course to its predecessor.
Mechanical factors leading to inconsistency
- Ammunition Ammunition can vary considerably in quality performance and consistency. Old or indifferent quality ammunition, mixed batches or mixed bullet weights or loads unsuited to their rifle will all lead to poor results.
- Oil and Wet Oily or wet ammunition will give poor results and it will not shoot to where the rifle is normally zeroed. Equally oil or water in the bore can both very breech pressures considerably, which will lead to erratic shots. The barrel should be thoroughly dried out before use.
- Powder Temperature Powder can deteriorate over time and burns faster at high temperatures or when under pressure in a reduced space. Ammunition should be regularly turned over and never be allowed to become hot e.g. by being left in the sun. Dented or damaged ammunition must not be used under any circumstances.
- Poor Obturation Powder gases must be completely sealed behind the bullet by proper expansion of the neck of the cartridge cases to fit the chamber tightly. Burn marks will be seen on the case shoulders if this does not occur.
- Headspace In rimless cartridges this is a distance from the closed bolt face to a datum point n the shoulder of the case. In rimmed cases it is measured to the front of the rim and in belted cases to the front of the belt. Incorrect headspace can cause excessive recoil and exert excessive pressure on the bolt lugs. Sings of incorrect headspace are normally black streaks running down the length of the case after firing.
- Barrel quality Heavy, stiff barrels will usually be more accurate than lighter ones but the latter will still give good results as ling as kept in good condition. Poor maintenance or can soon lead to a drop in consistency.
- Barrel bedding The rifle action should be rigidly fixed to the stock with mounting screws which must be kept tight. Most rifle barrels are "free floating" forward of the front mounting screw. If the action is not firmly bedded into the stock or anything e.g. the stock/after the fire’s fingers or anything actually touches the barrel itself, the barrel vibrations on firing will be erratic and lead to inconsistency. (To check if the barrel is free floating do the following- take a hundred rupee note or any other note and slide it under the barrel and the front stock/grip. The note should freely slide right up to the front mounting screws.)
- Irregular Muzzle and Bullet Base As the bullet leaves the muzzle the hot gases overtake it for a short period. If either the muzzle or the base of the bullet is irregular, the bullet may become slightly unstable until its spin corrects this. Use good quality bullets and do not damage the muzzle by poor cleaning technique for firing with grit in the end if the bore. As the last few inches are very important in relation with the round leaving the barrel.
This is a process by which the shooter adjusts his/her sights so that the centre of his/her group or Mean Point of Impact (MPI) coincides with a selected point on his target at a given range.
If the bullet is not to strike below the Point Of Aim (POA) situate some distance away, the rifle barre must be elevated to project the bullet slightly above the horizontal. This is achieved by adjusting the sights.
How to Zero
Zeroing is something that should only have to be done occasionally but it must always be done carefully. Between zeroing sessions, regular sighting shots should be taken to ensure that the sights still remain "on zero".
Do not try do zero in bad light, on a windy or very hot or very cold day.
To zero successfully ensure the following are available:
- Safe place with plenty of time and no distractions.
- A clean rifle with sights firmly attached and all bedding and mounting
- screws tightened.
- Plenty of ammunition
- Enough targets with a clear aiming point and or plenty of patches
- A comfortable lying position (prone)
- A firm, soft rest for fore end of the rifle and back of the supporting hand
- A small screw driver
- Notebook and pencil, Ruler
- Ear protection
Zeroing a 3 Shot
- When sure all shots will hit the target, fire a group of 3 careful shots at the aiming mark at the selected zero range. (In the army five shots are used for zeroing).
- The shooter's body should be well aligned with the target i.e. no strain should be needed to keep the sights on the aiming mark.
- Make full use of a good rest. Take exactly the same aim each time and try to make the minimum of body movement between each shot.
- If a bad shot is fired disregard it. And fire another one.
- Three good shots should fall close together forming a tight group at this stage it does not matter where on the target the shots fall but it is important that they should be close together.
- If the rifle and ammunition is of good quality, and firer competent, all shooters should be able to achieve a 3-6 cm or 1-2 inch group at 100 M with a good rest and in ideal conditions.
Mean Point of Impact (MPI)
The MPI of a three shot group may be established by joining each shot hole with a line and then drawing a line from each shot hole to the centre point of the opposite side of the triangle. All three lines should intersect at the same point within the triangle. This then in theory becomes the middle of the group or MPI.
For example if the three shots have all gone high and slightly to the left, the sight needs adjusting to right and down. After this a further 3 shot group should be fired to confirm that the rifle is zeroed in to the centre of the target.
It is always best to shoot from different range to see where the shot will fall on the target.
If zeroed at 100 M then shoot from 150 and 200 M. when at this range you will know where the shot falls and can adjust to hit the bulls eye.
Problems with Zeroing
If a tight group cannot be archived or the rifle cannot be zeroed in, then the fault can lie with equipment. However in most cases the fault will be found with the shooter.
To solve this problem a shooter should check the following (this list is not a complete one but a brief one).
With the shooter
- Take exactly the same and a precise aim for each shot.
- Wear glasses if needed.
- Follow through properly – try to see the shot hit the target.
- Avoid flinching or anticipating the recoil.
- Control your breathing try to be consistent.
- Squeeze the trigger rather then pulling the trigger.
- Fire from a comfortable position. (Prone)
- Making a proper use of shooting aids.
- Should avoid drinking alcohol before and during use of firearms and avoid heavy meal.
- The whole body should be relaxed and rested.
- Loose sight mounts or screws.
- Warped woodwork pressing against the barrel.
- Loose action bedding screws.
- Oily or wet ammunition.
- Very dirty barrel or one fouled with bullet residue.
- Poor quality ammunition or reloads (reloads are not done in India).
- Unsuitable bullet weight for the firearm.
- Barrel rifling.
- Trigger pull may be uneven or too heavy.
- Defective iron sights/scopes.
- Defective firearm
ENJOY A GOOD GROUPING
Bore sighting http://indiansforguns.com/viewtopic.php?f=22&t=10998