The weapon is currently a mere level 16 "rare" pulse rifle. However, the cutscene where it is rewarded to the player, and the weapon description itself, implies that the weapon is far more valuable and usefull.
I suggest remaking the Stranger's Rifle so that it can be upgraded like "Husk of the Pitt / Eidolon Ally / Necrochasm".
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I currently have "Time on Target" and "Starnger's Rifle". It seems that the "rare" Stranger's Rifle performs better than the "legendary" "Time on Target".