WELCOME!!!
I suggest factory ammo for your AR ONLY (no-reloads). American made ammo is the best ammo made, and that's not just my opinion. With that 1-9 twist you can shoot 55-68 grain without any problems. I always use Federal's American Eagle 55grFMJ and I can't rave enough about the stuff! www.ammoman.com is my favorite source- pick up 500 rounds today! First: READ YOUR OWNER'S MANUAL. Now read it again. There's really nothing to break in, just take your new AR, lightly apply CLP (I prefer Break-Free) to all the moving parts in the upper- the bolt, the carrier, charging handle and a squirt inside the two little holes on the right of your bolt and you're good to go. An AR's lower is truly Zero maintenance, don't worry about it. Before I shoot any rifle I run a bore-snake down it- excess oil in the barrel can be a bad thing (higher pressures go Boom). You MUST use USGI mags- you already knew that, didn't you? I suggest you get more than one for your session- if you get any jams with one try the others. For "break-in" just shoot normally. The moving parts will polish up and smooth out because it is a new gun. If it jams a few times the first 200 rounds or so this may not indicate a problem, again, parts are just smoothing out. It may NOT jam at all. If problems persist after you've shot 200-500 rounds come back here, describe the prob and ask more questions. You will need a special chamber brush made specifically for the AR- it will make cleaning a breeze. Also, buy a box of Q-Tips ans a few clean rags.
HAVE FUN!!!