bullet construction has a great deal to do with results
either rifle caliber we are discussing here,
will work if the proper anatomy and organs are destroyed
both bullet placement and bullet construction effect results
if the 243 was getting a better and more rapid initial expansion,
then the bullet you used in a 308 ,
it could easily produce faster-resulting lethality,
but that's most likely due to the bullet used ,
you can,t ignore physics,
a larger mass impacting at a similar velocity imparts more energy
I'm just stating that is been my experience that most guys using a 308 use bullets that do not expand as rapidly,
I see most guys use a 165-180 grasin bullet like a hornady, Remington core lock , with controlled expansion,
thus on less robust game like deer, the results tend to be less dramatic or rapid
swapping to a faster expending bullet has a very noticeable effect.
personally I see the SPEER 150 grain as about ideal, for deer

notice how the 70 grain 243 causes much more rapid impact results than a 168 grain 308 even if the 308 hits harder
no question the 308 would be less rapidly lethal on a perfectly placed lung/heart shot, but thats at the expense of much less penetration
if the 308 bullet is properly selected, especially if bones need to be busted,
keep in mind you don,t always get the ideal angle on the game or ranges you prefer to shoot at game,
having a bit of extra penetration potential in the rifle you carry is beneficial at times


https://www.youtube.com/watch?v=UDkO7BXX3WM

https://www.youtube.com/watch?v=3UnmfK_w9yI