Someone is going to say this eventually so I will.
Find out who the Age verification rep is in your area and get AV'd, then browse the Classifieds a little, find a few guns that are to your liking and in your budget, do a little research, reviews etc. Go from there.
Your choices are astronomical in the classifieds, especially if you are looking for an M4/16 variant.
Personally I'm not an armalite person myself, and I use an MP5 for outdoors, so literally any gun can be used outdoors all depending on what you are comfortable with!
Proud Supporter of Heckler & Koch Firearms