I guess it would be more of a barrel nut. For some reason I was thinking that my owners manual called it a choke tube, but I was wondering how that would've worked as one, since the threads are on the outside of the barrel.
Anyway, has shooting slugs ever caused damage to any of your saigas? I was just going to shoot targets with them, I don't do any hunting that requires a slug, so if it will possibly damage my gun, I won't shoot them at all.