CrystalShadow said:
Having been to the range several times, I can say that shooting pistols, bolt-action rifles, and shotguns are essentially unaffected when shot lefty. Though the bullets may come out of the right side of the gun for pistols, you're holding the gun extended in front of you and it won't obstruct anything.
For bolt-action rifles, you have to bring your right arm really far back to chamber the next round, but it's not too much of an inconvenience. Also, for trained snipers in video games, you would imagine that your own government/organization would give you a gun for your own handedness, right? Though I couldn't imagine using a lefty-bolt-action rifle after firing so much right-handed.
I have never fired an automatic or semi-automatic rifle before, so I can't conclusively comment on it, but I would say that, as far as I can tell, shooting a right-handed one while aiming would not be negatively affected by using the left hand. It would only be an issue if you were trying to fire essentially from the hip. Sure the shells are hot and could fall on your right arm, but I don't picture that being too much of an issue.
You would still imagine that the occasional enemy in a video game would use the left hand instead of the right, though.