1 . Minute-Of-Angle
The term "minute-of-angle" (MOA) is used regularly by target shooters at the range, but is probably understood, thoroughly, by few (the same goes for mil-dots). Defined loosely, one MOA = 1" @ 100 yards; so, if you shot your rifle 5 times into a 100-yard target and every shot went into a one-inch circle you had drawn on the paper, then your rifle could be said to shoot 1 MOA. Likewise, if every shot goes into a two-inch circle at 200 yards, then you're shooting 1 MOA. A 10-inch group at 500 yards would be 2 MOA.
Now for the fun part. There are 360 degrees in a circle. Each degree can be broken down further into minutes. There are 60 minutes in a degree. Likewise, there are 60 seconds in a minute. Now, to figure out the distance subtended by 1 minute at any particular distance, we need merely to plug those two values into a simple trigonometric equation. The tangent function fits the bill nicely. Here's the equation:
tan(angle) = distance subtended/distance to the target (units must be consistent--e.g., 1/36 of a yard [1"] divided by 100 yards)Now, we know the angle (1 minute or 1/60 of a degree) and we know the distance to the target (100 yards), but we need to figure out the actual distance subtended at the target (i.e., is 1 MOA actually 1" @ 100 yards?). What we need to do is solve for "distance subtended."Here's our final equation: tan(angle)*distance to the target = distance subtended
Make sure your calculator is in "degree" mode (as opposed to "radian" or "gradian") and type in 1/60 (for degrees) and hit the "tangent" button.Then multiply that by 100 yards. This should give you the distance (in yards) subtended at 100 yards. Multiply this by 36 to get inches. The answer should be:
1.047197580733" ,This is just a hair over the commonly quoted "one inch." At 1000 yards, this would be almost 10 1/2 inches. Apparently, it is just a coincidence that 1 MOA happens to be REALLY close to 1" @ 100 yards. It is, however, quite convenient.

2.The Mil-Dot
The "Mil" in "Mil-Dot" does not stand for "Military"; it stands for "milliradian." The radian is a unitless measure which is equivalent, in use, to degrees. It tells you how far around a circle you have gone. 2 PI radians = 360 degrees. Using 3.14 as the value of PI, 6.28 radians take you all the way around a circle.
Using a cartesian coordinate system, you can use "x"- and "y"-values to define any point on the plane. Radians are used in a coordinate system called "polar coordinates."A point on the plane is defined, in the polar coordinate system, using the radian and the radius. The radian defines the amount of rotation and the radius gives the distance from the origin (in a negative or positive direction).
ANYWAY, the radian is another measurement of rotation (the degree/minute/second-system being the first). This is the system used in the mil-dot reticle. We use the same equation that we used before, but, instead of your calculator being in "degree" mode, switch it to "radian" mode. One milliradian = 1/1000 (.001) radians. So, type .001 into your calculator and hit the "tangent" button. Then multiply this by "distance to the target." Finally, multiply this by 36 to get inches subtended at the given distance.With the calculator in "radian" mode, type: tangent(.001)*100*36 = 3.6000012"
So, one milliradian is just over 3.6 inches at 100 yards. If we extrapolate, two milliradians equal about 6 feet at one-thousand yards. You'll see the importance of this, shortly.
3.The Mil-Dot Reticle
The mil-dot reticle was designed around the measurement unit of the milliradian. The dots, themselves, were designed with this in mind and the spacing of the dots was also based upon the milliradian. This allows the shooter to calculate the distance to an object of known height or width. Height of the target in yards divided by the height of the target in milliradians multiplied by 1000 equals the distance to the target in yards. For example, take a 6-foot-tall man (2 yards). Let's say that the top of his head lines up with one dot and his feet line up four dots down. So: (2/4)*1000 = 500 yards away. This same tecnique can be used to estimate lead on a moving target or to compensate for deflection on a windy day.The distance from the center of one dot to the center of the next dot is 1 milliradian. We are told (by the folks at Leupold) that the length of a dot is 1/4 milliradian or 3/4 MOA (Given this much information, one can determine that the distance between dots is 3/4 milliradian.).* I use the term "length" because the mil-dot is not round. It is oblong. The "dots" on the verticle crosshair run oblong in the vertical direction. The dots on the horizontal crosshair run oblong in the horizontal direction (i.e., they are lying on their sides). The width of each dot is an arbitrary distance and is not used for any practical purpose. Like a duplex reticle, the mil-dot reticle is thicker towards the edges and uses thin lines in the middle where the dots are located and the crosshairs cross. The distance between the opposite thick portions is 10 milliradians.

4.First focal plane reticle riflescopes

5. How to Zero A Rifle Scopes for Air Rifle Shooters?

6.Pre-zeroing riflescope

Pre-zero sighting can be done either manually or with a bore sighting collimator,to bore sight manually,open the action of the firearm,If your riflescope has an adjustable objective or side focus dial adjustment turret,rotate the parallax ring/dial adjustment figure to the 50 yard position,Set variable-power scopes to mid power.

With the firearm in a steady rest position,remove the caps from the windage and elevation screws.Adjust the windage and elevation screws to position the reticle on the center of the target.For windage adjustment,turn the windage adjustment screw clockwise to move the point of impact right and counterclockwise to move the point of impact left.In the same manner,adjust the elevation by turning the elevation adjustment screw clockwise to lower the point of impact and counterclockwise to raise the point of impact.

If a large amount of adjustment is required tp align the reticle,make approximately one-half of the required windage correction,then approximately one-half of the required elevation correction.Finish by applying the balance of windage and elevation correction,

NOTE:When using windage-adjustable rings,make major windage correction with them,Final adjustment should be made with the scope's internal adjustment system.

7.Outdoor Products' Ten Shooting Safety Rules

1. Always keep the muzzle pointed in a safe direction . There are several safe "carries" depending on the situation. NEVER ALLOW THE MUZZLE TO POINT IN THE DIRECTION OF A PERSON.
2. Treat every gun as if it were loaded . You can never be positive that you were the last person to handle the gun. Never take anyone's word about whether or not a gun is loaded. Always check a gun to see if it is loaded when removed from storage or received from another person. ALWAYS TREAT A GUN AS IF IT IS LOADED EVEN IF YOU KNOW IT ISN'T.
3. Only load or cock a gun when you are shooting. A loaded gun has no place in your home or other place.
4. Check your target and beyond your target . Be sure all persons are well clear of the target area before you shoot. Check behind and beyond your target to be certain you have a safe backstop and that no person or property could be endangered.
5. Anyone shooting or near a shooter should wear shooting glasses . Also, all other persons should remain behind the shooter.
6. Never climb or jump with a gun . You can't control the direction of the muzzle if you stumble or fall. You should safely lay the gun down or hand it to a companion while you climb or jump over anything.
7. Avoid ricochet . Never shoot at a flat hard surface or at the surface of water. Ammunition can ricochet off of water just like a skipped rock.
8. Keep the muzzle clear . Never let anything obstruct the muzzle of a gun. Don't allow the muzzle to come in contact with the ground.
9. Guns not in use should always be unloaded . Keeping guns unloaded when not in use is critical to the safety of you and others. When you are finished shooting, put the trigger safety in the "on" position and unload the gun. Store guns so that they are inaccessible to untrained shooters and store ammunition separately from the gun.
10. Respect other people's property . Whether you're target shooting or hunting, if you're a guest on others' land, you should leave it exactly as you found it.