True assault rifles are some of the most difficult things to get your hands on. All automatic (which include burst fire) weapons count as machine guns under the National Firearms Act, and are highly regulated. No machinegun made and registered after 1986 can be legally transferred between civilians. Amongst other difficulties and regulation, that restriction means automatic weapons typically sell for enormous amounts.
The term you're looking for is 'assault weapon' which is a generally poorly defined term. Under the terms of the previous federal assault weapon ban, an assault weapon (rifle) is any weapon that has in addition to detachable magazines (a "clip" in popular culture), has at least two of the following features: a folding or telescoping stock, pistol grip, bayonet mount, flash suppressor, and/or muzzle mounted grenade launcher, as well as AR-15s, TEC-9s, Uzis, and AK-47s - those models being specifically named and banned.
Since we are looking at New York specifically, then the following apply. Rifles and shotguns ("long guns") do not require a state permit for purchase, nor registration, nor a license. Handguns require all three. There are additional restrictions on handguns that will typically limit their licensees to using and carrying them for sport. New York has an assault weapon ban in place, effectively continuing the expired Federal ban.