What i want to discuss is if it would be better suited to pair a bonded bullet with the 308 for large game over the copper bullets and reserve the copper bullets for magnum rifles?
I know people will say it depends on variables so for discussions sake lets assume the following: Bull Elk 450yrd shot what would be a more forgiving bullet choice? My 168g TTSX are getting about 2615 muzzle vel. with 22" barrel.
I'm not sure if we all have the same understanding of "forgiving bullet"... for example if you mean the range is suddenly very much less than your 450 yards? or if you mean you miss the kill zone?
At 450 yards, you have just enough for the manufacturer's demands, you are still doing about 1913 fps with 1365 ft*lbs. I have not seen a TTSX from a 308 WIN do anything unexpected at point blank either, so if you mean you are suddenly up close then no worries.
If what you mean is how much terminal effect there is with a different bullet versus a TTSX, then the thread will go long with all sorts of opinion and anecdotes about everyone's favorite. But since you asked....
If you gut enough elk shot with the TTSX at 450 yards from a 308, you will find less internal damage than when that same bullet is launched from a 300 mag. Velocity matters when it comes to the TTSX and so does placement.
When traditional cup-core bullets are studied in the same context, we will see similar trends, i.e., the 308 Win is enough at 450 when well placed, but just barely.
As often as not, the choice of the specific bullet between TTSX or one of the popular hunting bullets, will boil down to the one you like and will practice with the most. If picking a bullet means you don't practice because they are expensive and hard to find, then that is a good reason to go with one you can get and practice with more. When properly placed with enough velocity, they are all about the same.
When all is said and done, there isn't just one factor that simplifies these complex trades, but shot placement will top my list, ... and so getting and shooting enough bullets to keep your hit within a dinner plate is affected by that bullet cost/availability more than the slight differences in terminal performance. Pick the one you will not run out of in October.... and go get good with it. YMMV