Some of these posts are getting bit bizarre.
I have shot only one lion, through the top of the heart. Since this organ is farther behind the legs than for herbivores, there was no danger of breaking bone, except that it hit the elbow on the way out. The lion ran off about 30 yards and expired.
I used a .375 H&H. Based on my experience with other game of the same approximate weight, I think that almost any caliber from .270 to .458 would have had the same result.
If I were you, I would just keep the .308, given the total unlikelihood it would ever be necessary to use it for this purpose.
