marxman, Ultimately what you want is when the point of aim (POA) is the same as the point of impact (POI) at your desired shooting distance. The technique shown in the video assumes a few things that may not be true in your scenario ... namely the height of the optic above bore line, the ballistic characteristics of your ammo, and the desired zero distance.
I have a software program called Ballistic Explorer where you can plug all the variables in ... to include the ballistic coefficient of the bullet, bullet weight, muzzle velocity, wind speed and direction, humidity, temperature, altitude, barometric pressure, and scope distance above bore line. Once all these parameters are set, the bullet path becomes very predictable so you can actually see where the bullet intersects the line of sight at close range and again at the zero-in distance.
Here's a bullet path chart I just happen to have in Photo Bucket. It is for a 308 Win with a 168gr bullet ... sighted in at 200 yards and a scope height of 1.5". For this particular load, the bullet intersects the line of sight at 25 yards, reaches a peak trajectory of 2.5" at 112 yards, then starts dropping until the bullet again crosses the sight line at 200 yards. Each different set of parameters (scope height, cartridge specs, and zero distance) will result in different cross points where POI=POA.
If you post your specs, I'll run a chart for you. I'll need: BC of the bullet, bullet weight, muzzle velocity (measured, not estimated), actual distance from the center of your scope lens to the center of your bore, and finally, your desired zero-in distance.
marxman, Here's another example. This time it plots the same 223 Rem factory load (55gr FMJ bullet @ 3240 fps from a 20" barrel) sighted in at 100 yards.... the only thing different about the two traces is the scope height where the Red trace has the scope mounted 1" above bore line and the green trace has the scope mounted 2" above bore line. As you can see, the bullet path for the Red trace passes through the sight line at 55 yards and again at 100 yards. The green trace bullet path only passes through the sight line once at the sight in distance of 100 yards.
You may also notice what happens further downrange where the Red trace started out higher at the muzzle (-1") and ends up lower (- 6.6" at 250 yards). The green trace started out lower (-2") and ends up higher (-5.2" at 250 yards). These changes are strictly due to scope height so as you can see, it is an important parameter and has a significant impact on trajectory.
Another important issue is ... the previous chart with the 308 Win cartridge was sighted in at 200 yards whereas this one for 223 Rem is sighted in at 100 yards. This makes a very significant difference as to where the bullet crosses the sight line.
If you are having trouble figuring out the chart ... this may help: The blue numbers on the left side are in inches that represent the downrange path of the bullet. The "zero" blue dotted line represents the sight line. The numbers at the bottom represent distance in yards. When this chart is plotted on a computer, you can use the mouse to locate the cross hair at any distance or height as indicated by the number under the word "Crosshair", which is meaningless in this chart because I didn't set the crosshair on anything significant. In the previous chart, the cross hair was set on the bullet path (2.43") at 100 yards.
Knowing your actual velocity is essential fr this to work.
I used the bullet manufactures stated velocity and could not hit at the 200 yard target. (Zeroed at 50) When I actuall chronographed this round, I found the velocity was around 600fps slower than stated.
Using the correct info, I was able to compensate fr the slower bullet to hit at 200 and 300 yards.
My 50 yard zero gave me a bullet path that intersected again at about 175 yards, not 200.
I am operating from memory here so the exact numbers were slightly different.
The point of this is, you need the bullet bc and the ACTUAL velocity to make this work.
Clyde, You reinforced the whole idea of the OP's original post .... you need to know several parameters before the concept in the video will work. As it stands, the video is bogus because they do not take these parameters into consideration. The parameters include: bullet weight and ballistic coefficient, plus the bullet's actual muzzle velocity. Finally, you need to determine what distance you want to zero the scope. From there, a ballistics chart can be generated that will show the bullet path from the time the bullet leaves the muzzle until you reach the limit of the chart. In the charts I generated, I used 250 yards as a limit, however the software will also allow a range limit of 0~500 or 0~1000 yards