You get lucky with hawthorne engrams... specifically the higher tier ones (tier 1 drops current loot) ....there should be a few types of engrams; crucible ops could drop last disciple/disaster corps, pinnicle ops could drop bushido while everything else could drop techsec or smoke jumper. Each engram could drop a respective weapon... so you need to get lucky!! Save up some hawthorne engrams and blast through a load; probably won't increase your chances, but I just prefer doing them all at once rather than one at a time.