Congrats! I have the same rifle (except somebody at Cabela’s put some aftermarket parts in it) and i’ve changed a couple things.
1st, your carrier IS shrouded, i’ll guarantee it. IThe skirt length is not as short as a Colt sporter but not as long as atrue M16 carrier. You can use a D-Fender ring under your extractor and keep the blue one. (I never had a single problem with the blue one but I just shot it at the range.) The rear sight will always have that leftiness unless you have White Oak Precision add 2 posts to keep it straight (only need this for high end competition guns.) In terms of break-in, unless you’re shooting really dirty ammo, don’t clean your gun too much for the first 500-1000 rounds. The chrome-lining in the barrel and chamber needs to get itself polished up and slicked up. This is the Bushmaster-approved way to break in their rifles. You’ll probably want to replace the stock, buffer, and receiver extension.
Before you go buy railsand stuff you should really shoot the snot out of it. The only mods I currently run are a KNS globe sight, trigger, stock, and handguards. What everyone is saying, and listen to the pros like USMC03, L.K.Davis, Grant, M4arc, gotm4, and pretty much any mod or industry professional, is that we should start getting back to basics. I admit that when I see an un-modded 20" A2/A4 or a stock carbine it really gets me going. Sure all those fancy rails and stuff are impressive but the basics are sort-of the rifle’s legacy feature.
Pretty much just shoot it, love it, keep it lubed (well lubed,) play with it in your spare time, practice trigger control, spend tons of money on ammo and magazines, maybe get an optic and bipod (the harris #5 adapter will need to be modded to fit.)
It’s awful tempting to snuggle with it and sleep with it but dont. Your wife/significant other might not appreciate it. And be sure to spend about as much money on your special someone as you do on your rifle.
Such beautiful rifles…
Anyway i’ll get off the throne. And if anyone with more experience contradicts anything I said, trust THEM.
Again, grats! You will LOVE your rifle. And if you dont; i’ll love it for you at no charge! 