On my current playthru, I come across a Hunting Rifle Scope mod at the Gun Runners, as well as a rifle. So I decided what the hey, let's give it another shot. Lo and behold, I'm http://masseffect.wikia.com/wiki/Garrus left and right now.
Now I got to wondering... Why? Why did my aim svck with the hunting rifle ironsights, but it's shoot-a-tick-off-a-deer-at-100-yards accurate with the scope?
I decided to do some investigating. There is a completely harmless (actually sometimes helpful) bug where if you aim down sights while in 3rdperson view and then switch to 1stperson while still aiming, the HUD crosshair persists. This is useful for finding out just where on an ironsight the actual aim point is. This revealed something: the iron sights are literally off-kilter. No wonder I couldn't hit anything!
http://img259.imageshack.us/img259/3331/huntingriflesightbug.jpg It wasn't noticeable with the vanilla zoom settings, so I made a mod that altered the SIght FOV value to 10. I am crouching, I used the console to modAV my Guns skill to 100 and I took a Steady chem for the screenshot, to ensure maximum steadiness for the screenshot.
I thought it was maybe the SightingNode off-kilter. I checked the basic unmodded hunting rifle mesh. It was off-kilter, but not horizontally like in the screenshot. So that means the ironsight animation itself is off.
I checked the Varmint Rifle and This Machine as well, and they're off-kilter too.