If you plan on re-rolling the perks for any of the IB weapons buy two of said weapon. This may be expensive but if you are serious about re-rolling it will pay out. Roll one weapon until you get a fairly descent set of perks and then roll your other one until you get better perks. This way you never miss out on that good roll by rolling the same weapon again. You can repeat the process until you either run out of motes or find the perfect roll either way you will win in some fashion. Hope this helps If you already knew this strategy then you are obviously a wise guardian.