You are going to have to examine both mods and figure out what changes Khaine has made to his mod. I do know that Khaine has heavily changed the perks and crafting elements of the game which will affect this mod.
In this case, it is tied to the shotgun perk that Khaine is using. In vanilla, it is perkBoomstick which if you look at the tags in both the shotgun and ammo, it will have those in them. With Khaine's mod, you would need to add those custom tags he has for shotguns to the items in Izayo's mod.