see? no probs.
you'll find on most AR's, there is always something that feels LOOSE. Whether it be the extendable stocks, the handguards/rail systems, and on some even the upper to lower receiver fit. It's just the nature of the beast. Now, alot of that changes with modifications or manufacturers, too.
Magpul came out with their CTR stock, which still has 4-6 position extension (depending on which buffer tube you have), and locks in each of those positions like any other extendable stock. But they addressed the rattle or looseness that some feel with the traditional extendables by adding a Friction Lock, a second lever that tightens up the fit of the stock at whatever position. No more rattle or loose fit.
Rock River Arms, tightened up their tolerance of the upper to lower receiver fit, so they have one of the most rattle free fits around. No, they aren't the only one, but one of the more affordable ones.
Same with handguards and rails. When you go to a Free Float system, you'll most of the time get away from the Delta ring, weld spring, and snap ring all together, and normally - things will be alot snugger with the installation - and again, no rattles or looseness.
A lot of folks like the extra play though. Specially in the upper to lower fit, as it makes taking the gun down (removing the pins) a lot easier. And a little play in the action is more forgiving, in case you get some grit or grime in there - (just take a look at the fit on an AK
) But they'll fun forever.
So, stop worrying, and hopefully you are in a part of the country that isn't in the coming of the next ICE AGE right now, and go out and enjoy your gun.