Bob,
Actually the "hunting" Ballistic Tips don't have thin jackets, except just behind the tip. The rear of the bullet has a heavy jacket (in some VERY heavy), the reason the jacket often ends up looking exactly the one that killed this buck--like a widely expanded bullet. Since the jacket of hunting BT's normally weighs 50-60% of the bullet's original weight, they normally retain 50-60% of their weight.
It's pretty much irrelvant whether the core stays in the jacket, and it usually doesn't--though it almost always does end up with the jacket, if you recover the bullet, meaning it went along for the ride.
A lot of people judge cup-and-core bullets according to Bob Hagel's statement that "if jacket and core separate, penetration soon ceases." In my experience that is far from always true, whether with thin-jacketed, hard-cored bullets or bullets like the Ballistic Tip, with thick-based jackets.
