В процессе Ice Hammer is dealing less damage than it supposed to do

[Smerfny Jerz]

After acquiring the "Ice Hammer", I wanted to test its damage. I tested it by striking it hundreds of times on a dummy with 0 defense, and it turned out that the "Ice Hammer," despite its better stats (400 damage and a weight of 12), deals around 200 less maximum damage to the dummy than the "Bonebreaker" hammer (320 damage and a weight of 12). I should add that I tested it multiple times, striking the dummy several hundred times with both weapons. The sharpened "Sihil Silver Runeblade" sword (386 damage and a weight of 8) also deals more damage than the "Ice Hammer." Why does the "Ice Hammer" deal less damage than both of these weapons?
I'm including photos of all of these weapons.