Everyone knows .243 is basically a splitarse round.6.5 man bun are maximum age, what?, 2009ish?
Probably loaded somewhat hotter in factory ammo as a result, since 243 must be all of 60yrs old potentially in the same age rifles.
Both will kill deer. I shot my first moose with a 243, not ideal, but what I had. Any advantage by the 6.5 man bun, isn't worth spit until past 500yds. If you don't reload, and predominantly will shoot long range targets.....manbun. Anything else, call heads or tails.