We had a hard time getting my buddys 30-06 M77 to shoot decent groups too. We eventually tried the Barnes Tsx and they worked the best as far as accuracy, however we never tried the corelocks.
I think the barnes tsx bullets are the best out there and I use them exclusively now. I have shot deer, bear, and elk with them so far and all have been a fast clean kill.
I shot my 5 point Elk this year with the 140 gr. tsx out of my 270 thru the shoulder at about 100 yards. He lunged forward and died quickly. The bullet passed all the way thru without blowing out a bunch of meat.