Use the internal dmg proc relic, not the kinetic one as kinetic is effected by armor.
I'm seeing some numbers thrown around that the kinetic is better than the internal one for Mercs/Commandos due to the high amount of armour pen they have. Marginally anyway. And elemental for Pyro PTs/Assault Vanguards.
Basically the thinking is, which one to use should be based on what your talents are buffing.