Blunt damage does no bonus damage to armor, it just ignores %50 or %40 of the armor. Have you ever seen the difficulty value? And weight is not that high I think. The current throwing hammer has 6 weight per a stack of 3, which means one throwing hammer has 2 weight. As it can be seen from it's name this one is heavier so it is 3. Ehh it is 2.5 now. And knockdown is the reason why such an item is supposed to be. Please note that knockdown does not happen always.
According to your comments let me remake it:
Missile speed : 17
Weapon length : 61
Weight : 5 (2.5 per one heavy hammer)
Accuracy : 99 (decreased by 1)
Difficulty : 8 (it takes 24 STR now)
Speed rating : 81 (decreased by 3)
Max Ammo : 2 (a second chance to hit someone, or knockdown someone)
Slots : 1
Blunt damage : 40 (believe me it's not more powerful than a jarid)
Has no bonus damage against shields unlike many
Knockdown or at least a stunlock (the stun which polearms does)
Secondary mode:
One handed
Melee damage : 33 blunt
Speed rating : 94
has no thrust attack
Please note down that knockdown does not kill or maim everyone in a huge area. It just disables someone for a very little while. And does not happen always, in fact it has a very low chance. Before commenting on, I invite you to examine other throwing weapons.
Edit: And oh I must add I am no modeller, I humbly apologize for that. But it looks like Mjollnir.