A key point from the Event Faq on their website (
Halo Outpost Discovery | FAQs) is:
They then list some guidelines "you can assume will apply," including that "Replica firearms made from metal, solid resin/plastic/rubber are not permitted. " But there is still that first, most important caveat that the Security Staff for the Event and Event Center will have the final say at the weapon/prop check in.
When they say "Replica Firearms made from metal, solid resin/plastic/rubber are not permitted" they might mean exact firearm replicas, with out the orange tip or plugged barrel or being rendered inoperable. I am sure that as long as your item, foam especially, has been rendered inoperable if its airsoft or BoomCo based, and has an orange safety tip and plugged barrel, you will be allowed in with it.