I see this point raised by 2nd Amendment advocates often, that an AR-15, or any semi-automatic rifle with a magazine, is not an assault rifle. According to who? The NRA? Allowing them to define what constitutes an assault weapon is the equivalent of me defining myself as smart and handsome. 

While you may not consider it an assault rifle by your strict definition, the widely accepted definition does.

Definition of assault rifle https://www.merriam-webster.com/dictionary/assault%20rifle

:  any of various intermediate-range, magazine-fed military rifles (such as the AK-47) that can be set for automatic or semiautomatic fire; also :  a rifle that resembles a military assault rifle but is designed to allow only semiautomatic fire