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Old 01-27-2010, 11:47 AM
ar15barrels's Avatar
ar15barrels ar15barrels is offline
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Default How to use your scope

I'm working on a new thread and would like comments before I finalize it and have it stickied.

About bullet drop.
We know that the bullet drops as it travels down range.
Ballistic calculators will tell you how much the bullet drops if you give them all the proper data to calculate it.
Our scope's line-of-sight is above the barrel by an inch or two.
Gravity starts acting on the bullet as soon as it leaves the barrel.
Therefore, we have to point the barrel up in order to reach our 100yd zero.
This is to account for both the bore to scope height as well as bullet's drop from the line of departure.
This will cause the bullet to cross the line-of-sight around 85-90yds on a typical 308 load and then drop back down to your exact aiming position at 100yds.

When you are turning the scope knob, you are moving the reticle around within the scope.
Since we use the reticle to POINT the gun, what we are really doing is changing where the barrel is pointing.
So, we are using the scope's knobs to change the ANGLE of the barrel in relation to the line-of-sight.
This is really important to grasp because everything references back to the angle that you launch the bullet.

In order to hit targets that are farther away, you have to point the barrel up some more.
The graphic below calls the barrel angle the "line of departure".

With a 200yd zero, the bullet is probably crossing the line-of-sight around 50yds.

Last edited by ar15barrels; 04-06-2010 at 11:05 PM..
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