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This probably isnt the right place to ask, but just correct me if I am wrong.

For 30k they're Breacher Siege Squads and in the standard Legion list.
For 40k you can use them as Tactical Marines with Siege Mantlets from the Siege Assault Vanguard list (http://www.forgeworld.co.uk/resources/fw_site/fw_pdfs/Warhammer_40000/Siege_Assault_Vanguard_Army_List_Update.pdf).

I think you can re-roll failed armour saves (maybe just of 1) for Marines..

For 30k you get an Invulnerable save, like Combat Shields.

For 40K you can re-roll failed saves (rules are in the linked PDF).

Thank you guys! Time to convert that army to chaos!