>>76814853 (OP)
Dumbbell or kettlebell clean and press or snatch for very high volume or time. I say dumbbell or kettlebell because you want your arms in the scapular plane instead of linked by a bar, in case you have a type II or III hooked acromion. You need lots of volume. Shoulders are originally postural muscles from when we were knuckle walking and swinging from trees and need lots of volume to grow.
Honorable mention to heavy club and mace work but a) that's mostly assistance b) you need to do it for time and c) most people don't have the equipment, or what they have (eg a sledgehammer) isn't heavy enough for anything other than soft tissue/joint prehab and conditioning