Did I at any point mention deer at 300 yards? I think not! Well all I can say is the legendary pro stalker Jok Black said the .243 was his favourite round for reds ever, a 6.5 has only a bit more energy than a .243 with some bullets, and less with others, and as for that legendary trajectory, yes I agree it will hold its rainbow/mortar like ark very well
100 grain .243 has the same energy at 200yds as a 130 grain 6.5x55SE (both circa 1,500 ft lbs)! The .243 also has 400fps more velocity. So absolutely no ballistic reason why .243 wouldn't kill as well as a 6.5x55SE at 200yds, in fact on some deer forums, some people actually suggest .243 kills better than 6.5. So it appears opinion varies. I'm, guessing given the ballistics, any difference therefore is probably a matter of perception / preference.
6.5x55SE is noted for it's inherent accuracy and has long been a favourite with target shooters. However, there are examples of .243 being used to hit targets (non animate) at over 1,000yds, and .243 has marginally less drop, so I'd suggest any small difference in accuracy is probably not going to make any difference on a boiler room target area the size of that found on a large deer.
So unless you want to shoot very heavy rounds at distances beyond which you should sensibly shoot live game, any difference between the two is more likely down to preference, felt recoil, noise, cost etc rather than terminal performance which if anything is in .243's favour given the velocity, at least with bullets under 150 grains.
Edited by Alsone, 06 May 2016 - 11:10 pm.