What is legal? Well, ‘semi-automatic’ rifles, pistols and shotguns are legal to possess. What does that mean? ‘Semi-automatic’ is one trigger pull, one round fires (self-loading). Some might immediately respond, ‘So what, it will fire as fast as you can pull the trigger.’ Yes, you are right in that regard. However, the point is that semi-automatic weapons have been around for approximately 150 years and have been commonly used for hunting and sport most of that time.
The military’s M-16 (fully automatic) has a civilian counterpart called the AR-15 (semi-automatic rifle). They look the same, but they are not. Many hunters like the AR-15 for various reasons – principally for its durability. On the other hand, most hunters would prefer other semi-automatic rifles and/or shotguns for their craftsmanship, quality, and performance.
Addendum: Above Photo: Top is a common semi-auto hunting rifle. Bottom is the semi-auto AR-15.