Why would installing a M16 BCG in an AR15 be advantageous? What's the advantage of installing a bolt from a full-auto rifle into a semi-auto rifle?
I'm not being sarcastic or facetious in any way, I really am curious to know why.
What dragon88 said. In addition, it smooths out the recoil pulse. Of course, changing to a mid-length or rifle-length barrel would help in this regard even more (not to mention improving the sight radius for iron sight usage).
MPDC suggested a trigger change, and that's a good idea too, but you can also get away with just changing to JP yellow springs, and the trigger will improve a lot just by doing that.
So there you have it - three better mods than changing to a fully chrome BCG.
0) M16 BCG with action spring/buffer
1) Trigger (cheapest if you just change springs)
2) Mid-length barrel (the most expensive of the three, because you also have to change hand guard and gas tube)
For what it's worth, I've done the JP yellow springs and M16 BCG to my M&P15, and I like it. My next change will be to a mid-length barrel. I already have a mid-length MOE hand guard for it, but I might just get a floater instead.