Going to attempt to explain some about riflescopes here and not get to technical in the endeavor.
Basically there are 2 types of scopes and some sub-types in each.
FFP, First Focal Plane, this being that the cross hairs is etched in the first focal plane of the scope.
With the cross hairs etched in the First focal plane, it simply means that if you have a 4-16 power scope and you sight it in on 10 power at 100 yards, when you go from 10 power to 16 power or 10 power to 4 power the cross hairs adjusts size in relation to the image in the scope. So if you have a target at say 300 yards and you dial the scope into 16 power because you are blind like me then the cross hairs are adjusted to the target and the strike of the round stays zeroed.
Drawback, The cross hairs tend to get bigger at higher power and can cover over your target area and sometimes blocking out enough target so you cannot get a tight group. If you get a scope with very fine cross hairs to compensate for the enlargement of the cross hairs at higher magnification then the hairs may be too fine for good target alignment at lower settings. (You just need to find the happy medium in cross hair size).
Note here it really is not the cross hairs getting bigger, they stay the same size in the retical, with a target further out in the view it just seems that the cross hairs are bigger and cover more of the target when the hairs are still the same size.
SFP, Second Focal Plane, this being that the cross hairs etched in the second focal plane of the scope.
With the cross hairs being etched in the Second focal plane, it means that if one say has a 4-16 power scope and you sight it in at 100 yards on the 10 power sitting when you go from 10 power to say 16 power or from 10 power to 4 power the cross hairs stay the same size.
Drawbacks, The relation of cross hairs to target size differs, so your strike of the round will be off. So whatever power you sight the scope in for is the power you shoot it at.
Why is this important? Because many people want to shoot long-range target, (400-1000 yards). If one does not understand the function of a scope then all you will do is waste ammo and money trying to hit a target way out there.
In almost every scope you can find any combo of the Sub-category and Sub-Sub-Category, along with differing types of cross hairs.
One question I get from some people is do I need a Mil-Dot to shoot long-range targets? My answer is most times NO you don’t. The purpose of Mil-Dot is to find the range of a target, but most long-range targets are already fixed distances at the range. So no need to calculate distance using mil-dots. The other use for mil-dot is hold over, which is nothing more the Kentucky windage, but the dots/lines help to make a quick shot on moving game/zombies.
How ever most people will never be shooting zombies moving in cars or even running so the need for hold over on targets is not there so much at the range, unless you are bucking the wind.
Another question I get some times is which power range of scope do I need? And that is a good question, the answer depends on how far are you going to realistically shoot? Some say you need about 1 power for every 100 yards that is a good gauge for starting off.
In my opinion if you are going to shoot 300 yards or less a good 4-12 power will do the job. If you are going to shoot 300-600 I might say a good 4-16 or 6-24 power. Anything over 600 yards and you may need something in the 4-16 to 8-32 power range.
(One does not need a large power scope for shooting targets at great distance, as long as you can see the target in the scope you can hit it. The higher power lets one see targets way out there. It also let’s you power up to see where you might of hit the target at.)
Just a little note here and that is many pro shooters including some military and police marksman use a fixed 10 power scope for shots out to 500 yard range.
One of the most important things in a good scope is the optics. The better quality the optics and coating the clearer sight picture. The combo of good optics, large objective lens, larger tube and ocular lens allow for more light and good quality vision. This may be the most important thing when looking at scopes for your rifle.
I know we got other on the board that can fill you in on the what’s and wherefores of scopes better then I can so ask away and someone will answer.