Steve
I cannot help you with the exact specifics of how much parallex will throw you off at a certain distance as this depends on the design of the scope, magnification and parallax free setting of the scope.
I can however give you some general pointers.
The effect of parallax increases with magnification. This is why you will usually see parallex adjustments on most scopes capable of more than 11X magnification.
At about 6x or less the effect of parallex is probably less than a shooter is able to appreciate under normal conditions.
Most scopes which do not have a parralax adjustment are set at the factory to be parallax free at 100 yards or 150 yards. At closer or further ranges, some parallex may be apparant.
Some tacticle non parallax adjusting scopes may be set at the factory to be parallax free at 300 yards or 300 meters.
A non parallax adjusting scope may usually have its parallax free range changed by returning it to the factory or the owner my have a go him/her self.
Admittedly, a deer can look very small at 700 yards using a low magnification scope.
You may want to go with a variable scope giving you the option of high and low mag.
If this is the case, a general rule of thumb is to zero the rifle at your zeroing distance with the appropriate parallax setting for that distance.
Then decide your max hunting range. Set your parallex adjustment to two thirds of this range. Then if while hunting you forget to make a parallex adjustment, your scope will be optimised to give less parallex over your complete shooting range. In all cases use the lowest magnification you are happy with.
Parallax is also reduced by making sure your eye is properly centered on the scope eyepiece. Practice this so that it is repeatable accuratly from shot to shot and day to day. This is very important and a criticle part of marksmansship using any rifle scope combination.
Hope this helps
Regards
700
