Some of them do indeed have a lot of heavy jacket in the construction. I shot a deer a few years ago quartering hard away and the 168gr .30cal NBT would up in the neck, just under the hide. When I cut the hide, the jacket was there, with some of the lead core lying next to it. The remaining jacket weighed 69gr, which is a little over 40% of the original bullet weight, and this is after expansion, so I'd not be surprised if that bullet is actually close to 50/50 jacket/core. It's a great performer on deer and hogs at .308win speeds.
