Win .243 100gr SuperX Power Point>Energy @ 200yds--1332fp
Energy @ 300yds---1089fp

Like some said, keep it at 200yds and try head and neck shots.
It is still good for 300yds with less energy, but 900FT is close to
40 acres long. Practice hitting an 8" aluminum pie plate @ 900ft and
see how you do before you shoot any deer at 300yds with your .243.
If you use a scope with Duplex Reticle,next time you go to a sporting
goods store and they have a practice life size Archery deer, measure
one from Nose to Tail.Cut yourself a piece of Plywood to those measurements
and set it up to see where the sides of the Plywood touches the darker
post on the Reticles on scope.This will give you and idea of Deer distance
at a broad side.Best thing is to know some Archer that has one and will loan
it to you so you can do it at all angles and yardage using the scope Reticle.
This is with the scope set at it's lowest setting...3-9x44...set at 3.
Let's JUST say the plywood edges touched the dark edges of the Reticle @ 300yds.
If they pass the dark posts about an 1/8" or more @ 300yds, you know it is within your range.
You won't need a ranger finder scope or a hand held ranger finder.
Mount your rifle, look thru the scope and if it is past the dark post, take a deep breath
and squeeze the trigger.
I have one just for me and friends to use for getting an idea with different
scope Reticles.
The smaller the plywood gets,the further the deer will be,
but aleast you will have an idea how far you will be shooting.