It's an absolutely ridiculous assertion that a "tactical rifle" needs a detachable box magazine. Sure, it's all the rage and a very fashionable accessory to be sure. But necessary? Bull s**t. Unless you're competing in organized competition where the course is set up to favour mag based systems, then it's hardly worth the money unless you're totally in it for the LCF.
If you REALLY want a mag fed system then chose the Williams, AI, ATRS, Badger, V-Bull, or whatever. Take your pic. They're all decent. Boils down to personal preference.
I'm with the others regarding the factory barrel. Give it a chance before you spend $500 or more to fix a probelm that may never have existed to begin with.
If I were you, and had extra money to accessorize the rifle, consider spending the money where you'll potentially see the greatest initial benefit. Spend it on the stock! Yeah, the MacMillan A5 is a great stock but having the ability to adjust for cheek weld and length of pull will definitely be worth the additional money spent.