They are certainly among my favorite cup-and-core bullets as well, though I wouldn't expect performance like that every time. At moderate muzzle velocities (2800 and under) they will penetrate pretty darn well.
I have recovered quite a few Interlocks over the years, ranging from 130 .270's to 225 .338's. Recovered a .225 .338 from a whitetail buck that probably weighed 200 on the hoof, on a quartering away-shot at about 200 yards. The bullet entered the left rear of the rib cage and was found in the right shoulder, mushroomed back to the Interlock ring. Muzzle velocity was about 2750, as I recall.
Also recovered a 139 7mm from a broadside shot on a barren ground acribou bull shot at about 100 yards with a .280, muzzle velocity around 3100 fps. Same sort of expansion. My wife shot a pronghorn buck at the base the throat as it faced us at 100 yards or. Fund the 130 .270 Interlock under the skin on the back of the neck, pretty well mangled. That's the only one I've seen separate jacket and core, but they were together, and the bullet did go through some hard neck bone.
There have been a few others recovered, but most went on through. Probably I have recovered several Interlocks because my wife and I have shot a lot of animals with them!
