| I never had a problem with picking stuff off with the Sniper Rifle in enclosed areas. It is important to put anti-heat stuff on it though.
Currently using Combat Optics X, Frictionless Materials X, and Sledgehammer Rounds X on my HMWP X Pistol and HMWSR X Sniper Rifle.
I haven't used the Assault Rifle or Shotgun much on my Operative spec'd Infiltrator though as I have absolutely no bonuses to them and they're highly ineffective. I use the Pistol on the Thorian Creepers, Husks, and Rachni - but anything else I far prefer the Sniper Rifle on. The A.I. only makes it "silly" if you're bad at being an effective Sniper.
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