Question, what is the difference between a semi-automatic and a full-auto bolt carrier. Why would
you go with one over the other. Is there a difference in quality? Thanks.

Besides the physical differences obviously needed for full-auto, the M16 carrier is a little heavier.

Quoted: Question, what is the difference between a semi-automatic and a full-auto bolt carrier. Why would you go with one over the other. Is there a difference in quality? Thanks.

Semi auto bolt carrier is used with semi auto rifles. A full auto bolt carrier is used with full auto rifles. Some people choose to use full auto cariers in their semi auto rifles because of the increased weight.

edit: damn, beat me to it

And, correct me if I'm wrong; the back of the 16 carrier is ramped where the 15 is more squared off, it seems that the 16 carrier would have less impact on the hammer as it rides back. Also on the 15 carrier it appears that the firing pin is more exposed.  On one guys' AR,  it would fire a couple shots then hang up. You couldn't do jack with it except remove the mag, bang the butt on the ground to get it into battery ensuring a fired/empty chamber then pulling the rear pin and getting it opened up. Everything appeared fine. Close it, repeat, and it would eventually hang up again.  Finally figured out that the 15 bolt carrier left too much of the firing pin exposed and it would routinely hang up on the hammer (out of spec or collection of tolerances?). He sent it back to big A for a refund.