Stalker,
Human,
15 years ago
I never said that a pulse rifle wasn't powerful enough to put a predator down, after all, they blasted straight through xenomorph hide in Aliens with no problem, but it would more than likely take several direct hits to actually finish the creature off, as they are very resilient to injury. And how often do you really get a clear shot at a predator? In the movies, whole clips were emptied at them that simply ricocheted off their armour or missed entirely.
Shotgun shells fired from close range have the ability to concave large areas of soft tissue as the pellets tear through flesh. Even with numerous wounds like this, and an amputated hand, the pred was still not stopped in the second film.