Semi-autos are perfectly legal in ct assuming they dont have a couple specifics that I would lump into the "no-no list" : collapsable stock, flash suppressor, bayonet lug.

Easy thing to do...go to one of your local gun shops...if they are willing to sell it, then its legal to own in ct

Best bet would be something like the Smith and Wesson M&P 15-22. Awesome machine with a lot of the bells and whistles to make it seem like a true AR style rifle.