The 7mm first they beefed up the 140s for steel shooters and then for the 120s they shortened the 140s jacket which left them thicker at the nose. The 6.5 was purpose designed with the heavy and improved hunting BT jacket. The 6.5 jacket is thinner at the nose than the 7mm but not enough to make much difference. But of the two I would say the 7mm is tougher both from looking at the sectioned bullet and performance on game. As others posted it almost always makes an exit.

I will be using the 6.5 120 BT next time I deer hunt with my 6.5x55 and know it will perform as good or better than the 129 grain Hornadays I used last season. The Hornaday is an excellent performer. With either of these and a case full of R26 the little 6.5 is right up there with the 270 Winchester with 130 grain bullets, any difference would be hard to see in the field within normal ranges.

"When you disarm the people, you commence to offend them and show that you distrust them either through cowardice or lack of confidence, and both of these opinions generate hatred." Niccolo Machiavelli