The caber, being so long, sets the center of gravity off. Its more than just the weight that is a factor. Its length, the balance needed to throw it with skill needed to gain that all important "noon" and achieving the ground speed needed to actually turn the thing in the right direction are all to be taken into consideration.

I've seen a lot of caber tossing. Balance is key. You can usually determine how a caber is going to turn simply by the balance and control the athlete has before he ever makes the throw.