This seems to be a very popular weapon among mass shooters. High capacity magazines that can be taped back to back for easy reloading. .223 bullets that are lightweight and have high velocity do massive damage.

Not a sporting rifle by any means. No, not an assault rifle due to tiny tweaks made by manufacturers. Can be converted to full automatic by some minor reworking but not necessary.

Full background checks plus several day waiting period should be required. Possibly, this terrorist event would not have happened if the background check had turned up the domestic abuses and the FBI interviews before allowing the terrorist to take posession.