Years back in a similar discussion here, I got a Sierra guy to give some explanations.
Basically, Sierra's 150-grain SPBT and the 165-grain HPBT can be driven a bit too fast for best results at ranges under 100 yards or so. Excessive expansion; "blow up".
Once they are down to 2,800 ft/sec or less, they perform in what we could call a normal result for penetration and expansion.
The flat-based bullets are slightly heavier in construction in these weights and don't have an "overdrive" problem.
One time on my 500-yard range, I was down to my last eight rounds of 165-grain HPBT handloads for my '06. So, two four-shot groups. 0.8 MOA. They are indeed accurate little doofers.
Purely FWIW: The 150 Sierra made a slight dimple in the steel at 500. The 165, a bit deeper. But the 180 SPBT made the beginning of a crater, with a bit of back splash. I'd have no qualms about using the 180 on elk. And, the 180 gave me 0.4 MOA on my 100-yard range. (Not bad for an old rifle with some 4,000 rounds through it.)