My M4 with no choke tubes that is bored cylinder is a version deemed restricted in Canuckistan because of its short barrel and collapsible stock with the thing that goes up in the back, etc etc.I've bought several new, and all only came with 1 choke. Yours with no choke at all, is a fairly recent model? Had read they had changed one version (military issued I believe?) to a fixed choke.
My question and concern about the ones being sold now, modified choke tube only, is regarding how well they shoot slugs.