I think that the items are more centered towards spies/hansels. For this reason I have no idea. But I think i have figured out a possible theory of increasing your chance of getting the item. I believe that you need somewhere between 2-4 unloads on the EB to increase your chance for the item being yours. Also it might help to throw pots (potions). If you do all of this you should have the item in the end or at least a good bonus. I have no proof but this is what i think you need to do to get the equipment.
Slade; ive tried being extremely active and i have but i have no success. I unloaded 3 times on NML and threw some pots and got the arm plate
Ive also seen a fellow clan member do the same ( he is in a different clan now then when he got his item)
Here is my 2€, it is a lottery. The amount of actions you successfully do enters your name in that many times. In the end a certain amount of names are picked. So even if you only completed 1 action you have a chance. The more actions the better your odds, but some people are just unlucky.
Thank you! Makes sense... Theres probably a little more to it than that, but you cant ignore the devs!