You REALLY need to do some serious reading before plunking down money for a scope so you will know what you are getting.
Eye Relief: how far away from the eye piece (rear of scope) you can hold your head and still see the full view thru scope. Too short and you will get a scar over the eye when scope hits your head during recoil.
MOA: minute of angle, roughly 1 inch per 100 yds. Scope adjustments are quoted in MOA such as 1 MOA clicks. This means that 1 adjustment click will move the bullet point of impact (POI) 1" at 100 yds, 2" at 200 yds, 0.5" at 50 yds, 0.25" at 25 yds, etc.
You sight in scope at one specific distance depending on cartridge and intended use. You move adjustment dials to move bullet POI on target so that it will shoot to center of where you are aiming. Since scope is above barrel, the barrel is slightly raised above horizontal so the bullet POI can be adjusted to hit point of aim (POA) at a selected distance. This means, the bullet is actually rising above line of scope sight (even though falling from line of barrel) during part of its flight and then falls back downward due to gravity. Theoretical example for gun sighted in dead on at 100 yds:
- bullet is 1.5" below line of sight LOS) at barrel
- bullet first crosses LOS at about 10 yds
- bullet is 0.5" high at 50 yds
- bullet is dead on at 100 yds
- bullet is 1" low at 150 yds
- bullet is 2" low at 200 yds
- bullet is 5" low at 300 yds
Actual trajectory will depend on cartridge, bullet weight, load, barrel length, etc. but you should get the idea from this simple example.
