Hello there, Thank you for your report. The intended design for attunement is that it only works on weapons in the active loot pool, and when it is working you should have about a 50% drop chance for the weapon you selected from activity rewards. Multimach CCX is explicitly listed as one of the current Iron Banner attunement options, so it is supposed to be a valid target for Iron Banner attunement. There is also already a bug open for Iron Banner attunement not seeming to function correctly. That report specifically calls out players going multiple games without seeing their attuned weapon, notes player reports that attunement can feel like it is actually reducing the drop chance, and says attunement does not appear to be working as expected. So if you have Multimach attuned and it is still rarely dropping, that matches a known issue much more than intended behavior.