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What base sizes do Lootas need to be on?
I'm assuming meganobz and big meks are on medium bases while burnas are on the small.
Probably the standard infantry bases that are supplied in the boxed set, though you could go bigger if you wanted to; there's no rule disallowing changing the base, as long as you aren't trying to get a competitive advantage out of it (smaller bases than normal, etc.).
regular base should be just fine, as they are regular sized orks, the larger bases are for models that (AFIAK) their actual BODIES are larger than the average troop. so lootas with giant guns, may be big but don't need a larger base because the base is only to show how much room the loota takes up.
Well aware that you can go bigger and not smaller.. Thanks