Many people like that bullet. I have no experience with it.
Personally, in .243, I do not consider anything under 90Gr's suitable for big game. Sans the 85GR Partition and Barnes solid copper bullets. In many states the .243 is smallest legal caliber, why push it by using lightly constructed bullets.
The 85 HPBT is a hollow point. Hollow points are used to allow faster expansion. Faster expansion in an already too light bullet screams under penetration and over expansion with bullet blow ups likely. Slip that bullet between the ribs and you may well see lightning strike kills. But hit a rib and you may just shred the hide causing a huge wound that will likely still kill, but you also likely will not recovered game. In my humble opinion, we owe far more than that to the game we hunt. Use the appropriate bullet. Its generally accepted that all bullets under 90Gr's are varmint bullets. There are exceptions, but like I said why push it.
CW
Actually this is not true...The Sierra GameKing 85gr HPBT is a deer bullet...It's core is harder than most and the jacket is thicker...This allows the bullet to penetrate into deer before it starts expanding...So, not all hollow points are designed to expand rapidly...Bullet design also comes into play...This is an excellent long range deer bullet and will actually give more reliable penetration than some of the 100gr soft point bullets...
I realize the 85gr HPBT from Sierra is a game bullet, its not something I recommend for anything but specialized use. With a BC of .206 and a weight of only 85grains, IMHO, it is barely marginal. If it works for you and you like it, god bless you.
If you reread my post with attention to the bold/underlined statements, I think a truer intent and understanding will come to light.
CW
