Originally Posted by Tumbleweed
Probably 95% or more of the above scopes are second focal plane. Meaning- point of impact WILL change and change significantly at longer distances if a person changes the power settings around. When you zero the rifle at a certain magnification at a certain distance and make a drop chart it will work correctly at that magnification only. If the power is turned up or down from the original setting, point of impact will change. If we're talking about zoomed down in the brush at close range, it won't make any difference. However, at long range-watch out. Just something to be aware of.
I don't know what to make of your post. Are you saying that if I sight my rifle in at 400 yards using 10 power then turn then power down to 4 my point of impact at 400 yards will change?
If that is what you're saying and that's the way I read your post your ill informed.
It does not make any difference whether the scope is first or second focal plane. Once a zero is established on any power at any range the zero will remain the same throughout the power range of the scope. A drop chart can be generated using the rifles zero of 100 yards or 600 yards. The zero has nothing to do with the accuracy of a drop chart. The drop chart will reflect either a dial up or dial down or hold over or hold under depending on the zero.
Now if you're talking about hold over using MOA or Mill Dots then there is a difference between first and second focal plane scopes. The marks in a first focal plane scope are correct throughout the power range whereas in the second focal plane the scope usually has to be set to the highest power or at 50% and do the math.