Shattering impact on my rumbler has little to no effect

[Vodhawak]

First of all in the decription of the blessing there is a mistake, its brittlenes not rending.
Check on this post to get your answer:

Blessing Shattering Impact does not work correctly

Rending and Brittleness remove armor from enemies. If there is no armor to remove you don’t get a bonus from the attack. For the Rumbler’s Shattering Impact the situation might be that you are hitting a Crusher that a teammate is fighting in melee with. You stagger the Crusher and now all of your teammates attack penetrate the armor because of the Brittleness. You should see an effect with a Ogryn cleaver. Attacking it with the a Shattering Impact Rumbler and then with the cleaver. The direct…