More than one of us went through that same sort of experience with various bullets!
Core--Lokts were pretty thick-jacketed bullets back then (though not today), but they weren't "unbreakable," especially close up at higher velocities. In fact John Nosler developed the Partition after having problems with a British Columbia bull moose with 180 Core-Lokts from a .300 H&H.
I started using Partitions during the last 3-4 years of the lathe-turned bullets, the mid -1970s, and they took a lot of doubt out of my hunting--especially for elk in the thick timber of the Montana mountains alongside the Idaho Panhandle. A hundred yards was a long shot, and after switching to what were then called 200-grain "semi-spitzers" in my .30-06 there were no problems.
“Montana seems to me to be what a small boy would think Texas is like from hearing Texans.” John Steinbeck
