Guys and gals:
Red Dot Arms is running a special on M16 bolt carriers -- $99.00 complete, assembled and ready to go.
Don't freak that it is an M16 rather an AR15. It is perfectly legal to use in a semi-auto AR. (There is even an ATF letter on the subject which you can find out there on the Net.) Lots of shooters prefer using M16 bolt carrier assemblies because the slightly heavier weight reduces recoil. I have seen these in production and they look to this non-gunsmith eye to be top quality. From the last time I built an M4, $99 is a deal.