Can I legally put an m16 bolt carrier in my ar-15 without someone trying to accuse me of building a fully automatic rifle?  I want it for the added weight, and it just looks like it would stand up to more abuse.

Yes.

You're asking for legal advice from people who have nothing to lose if you make the wrong choice.

I think there is something about the M16 bolt carrier and how it works with the trigger group differently than the AR15 bolt carrier.  I haven't seen a M16 bolt carrier in a few years, so I don't remember the specifics.  But I recall something about the hammer hanging up on the AR15 bolt carrier if the disconnector is removed, where it doesn't on the M16.  With the M16 bolt carrier, if you remove the disconnector, it can operate full auto.  I wouldn't want to be on the wrong side of a "can be readily converted to fully automatic" argument over a $100 part.

Quoted: You're asking for legal advice from people who have nothing to lose if you make the wrong choice. I think there is something about the M16 bolt carrier and how it works with the trigger group differently than the AR15 bolt carrier.  I haven't seen a M16 bolt carrier in a few years, so I don't remember the specifics.  But I recall something about the hammer hanging up on the AR15 bolt carrier if the disconnecter is removed, where it doesn't on the M16.  With the M16 bolt carrier, if you remove the disconnecter, it can operate full auto.  I wouldn't want to be on the wrong side of a "can be readily converted to fully automatic" argument over a $100 part.

There is no operating difference when an M16 carrier is used in an AR15.

AR15 carriers are cut as to not be able to operate the auto-sear in an M16,(notch where the hammer hits the firing pin) and some are cut as to not operate a "lightning link"(the half circle carriers)

An M16 carrier does not make an AR15 fully auto, and never will.

I use one in my AR15 as I don't like the way the hammer rides the firing pin when the bolt cycles back.

If your rifle fires no more than 1 round with one pull of the trigger it's semi-auto.  If you haven't drilled your lower for a sear nor are using a DIAS or a RDIAS its still semi-auto if it fires no more than 1 round per each pull of the trigger.  In this case a M16 carrier is legal.  

If someone doesn't believe me please show me case law that says otherwise.

Please people.... search!

This comes up all the time... and has been discussed ad nauseum.

My two cents.... not a big deal.... but I probably wouldnt do it... because if there is this much argument in the knowing gun community, there is ten time the same amount of ignorance, in the LEO community.... and the reward does not balance with the potential risk.

www.ar15.com/forums/topic.html?b=1&f=6&t=147440

...by the way, i was kinda typing fast, i know it wouldn't make it fully automatic, I meant "attempting to build a fully automatic weapon", as the M16 bolt carrier is an important piece of the burst or automatic firing systems from what I know, and I've always been under the assumption you couldn't use ANY parts that are intended for automatic use, but obviously, not sure on it.  That was my question... hehe (one day i'll learn to proof read...)

wow... started to read that link on bolt carriers...  I guess i'll just stick with the ar-15 carrier... lol!  I can see it's a touchy subject with some people!  Thanks for the help guys, even though I have no idea if its legal or not, I at least know what would happen in a courtroom if my carrier was ever questioned!  Bottom line, NOT WORTH THE TROUBLE!!!