Re: Is it legal .
New York maintains a state level prohibition against the features listed in the now defunct Federal Assault Weapons Ban. Magazines made after 1994 with a capacity in excess of 10 rounds are banned, as are rifles with two or more of the restricted features (pistol grip, bayonet lug, collapsible or folding stock, flash suppressor, and threaded barrel)
NYS grandfathered firearms produced before the 1994 ban:
"So, the only remaining question is, was the rifle you're interested in made on or before 9/13/94. This is the "pre-ban" or "post-ban" question for NYS. If the seller is marketing the rifle as "pre-ban", then he or she should be able to produce either (i) a letter from Colt stating the pre-9/14/94 date of manufacture, or (ii) a serial number that you can verify places the rifle in the pre-ban manufacture period."
If you have any documentation proving that the rifle was manufactured before that date, you should be OK.
You don't live in NYC so the rifle doesn't have to be registered.