There is a lot of misinformation out there.
Last year, I emailed Sierra and asked them if there were any differences in construction between GameKing and ProHunter.
The answer was:
(a) you must compare apples with apples. e.g. compare two equal weight, equal calibre soft points, not a HPBT GameKing vs a soft point ProHunter;
(b) the soft point GameKing and ProHunters are manufactured exactly the same, on the same machines, with the same materials. So for a given weight, the construction differences are negligable to nil. The ProHunter is not designed to be a tougher bullet.
I've always said I wish Sierra had given their HPBTs a different name.
Phil Mahin at Sierra did say "Every now and again, I’ll get reports that our GameKings are more fragile than our Pro-Hunters (with all other things theoretically equal) and my theory for a reason is because there is less bearing surface on a GameKing. This gives the lead core less friction to lock into the jacket with, giving the impression it expanded quicker in relatively similar hunting situations."
If anyone wants to read the whole email response, pm me.