An Ion Shield halves incoming damage. Knights die to HP damage, so causing HP damage is the deal. Haywire - Crons with Storm Staffs deal 20 12" Haywire shots. Ace.
Melta with Armourbane needs a 4+ to penetrate side AV, which is 92% chance of occuring - if it hits - with the shield, that's 46% chance - and requiring 3 Melta to effectively remove 1HP. Normally, that would mean about 18 Meltahits to kill, and with 66% accuracy, that's 27 shots.
However, Ion Shield only effects one side. Sandwiching with melta squads gives you better chance of damage on one side - so there's a 150% multiplier on damage - rather than needing 18 meltahits, you'll need 12; or 18 shots. 2 Suicide 5 Man Terminator Squads is what 350pts with Combimelta, and 10 one shot meltas - for 7 hits, and 1 HP (50% save chance) + 1-2 hull points of damage for 3 HP damage. It's not brilliant, but the next turn, if you aren't shot to death (i.e have something else to distract), popping a couple of chainfists for an assault will strip a further number of HPs.
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