You'll be in the neighborhood of 8-10k for a lightning link or RDIAS, occasionally you'll find some M16 variant (usually oly's or frankfords) under 10k, colts go for a little bit more- most I've seen lately are 12-14k. Converting your AR15 to an M16 has been illegal since May 1986, unless you're a manufacturer. Even then, by doing so you'd be making the weapon illegal to own except by gov't/LE/dealer (as a post may sample to demo to LE/gov't agencies). Hope it helps.