ORIGINAL: MichaelT.
The .308 holds more velocity and retained energy at 200 yards + , but either will work.
Do what ?
Comparing bullets of the same sectional density i.e a 100 gr .243 to a 150 gr .308.
The .243 starts off faster and ends faster, it does not have the KE of the .308 ( about 200ft/lbs less@ 500 yds) but to bad energy doesnt kill.
The .243 is faster, flatter by about 7" at 500 yds, still pushing 2k fps at 500 yds, about 4" less wind drift at 500 yds.
.243 is the clear winnerat long range