BudsGunShop.com - is receiver actually 3.5''

Dennis, the Chamber is a 3" Chamber (Accepts 2-3/4" and 3' Shot shells), 18.5" Heavy non Chrome Lined Barrel that's Mobil Choke Tube Threaded. Cheers and stay safe!

So Trin is not getting that info from the manufacturer website because the manufacturers sight clearly says this has a 3" heavy barrel.
And no on the Chrome lining,
Full details on EAA website here
https://eaacorp.com/product/akkar-churchill-612-pump/
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Plus owners manual for additional info here
https://eaacorp.com/product/akkar-churchill-612-pump/#tab-ywtm_38494

YES, according to the manufacturer's website, this has a 3.5" Chamber. The barrel is neither heavy nor chrome lined. I hope this helps!