[jsimmons]

Just buy quality parts and you won't have any problems. The barrel actually determines whether or not you can shoot 5.56. If the barrel is spec'd for it, you won't have any problems.

As far as the lower itself is concerned, just buy one from a known manufacturer (and don't cheap out). I think you can get Spike's "blemished" lowers for less than $100. It might be a little scratched up, but it's still a Spike's lower, so it's okay. I also won't waste money on a billet lower because it won't provide any better functionality than a forged lower.

Further, if you're going to buy a part or two each paycheck, do NOT buy a lower-parts kit unless you're willing to settle for the hard parts it comes with (I learned that the hard way, and could have saved myself $40 if I had known ahead of time). You'll likely end up replacing the trigger and the pistol grip at the very least. If you *do* get a LPK, void the one from DPMS, the roll pins are over-sized and difficult to install.