I should clarify that there is only one way to actively block, and that is to have NO other weapons but your sword and shield equipped and pull your left trigger which will then block. This is where we run into a problem with Javlok Magazine Warp. You see, I then have to equip the Javlok to benefit from the synergy it offers Ack & Brunt... but then I can't actively block to take advantage of my Electromagnetic Shielding mod.