It varies from brand to brand.  If you dislike the rattle or wiggle, put the endpiece/ stock in a vise and heat it up.  Slowly apply pressure, and the heated unit will crush down a bit.  This will cure your rattles.

Remember when you do this that you do it a little at a time, your goal isn't to crush the stock, its just to put a slight bit of change in it.


Another option that doesn't work as well is to apply a strip of electrical tape to the buffer tube.

Quoted: So is the wiggle normal then? Cuz I thought mine was a little too much.  And what do you use for a heat source.  Also, what kind of tool do you crush with. Does this procedure leave marks/ugliness on my beautiful AR?

Heat it with a hair dryer, compress it in a vise lightly, pad the areas where the vise makes contact.  

It leaves no mark, and you can't tell if this process has been done or not when you are finished.