Are you seeing the same graph I am Mr. Silvers? It pretty nicely shows the 16-17" range as that point where the fps gain per inch of barrel really slows down. It looks like about 100fps difference, ±10, between a 16" and 20" barrel.
-B
16 is the sweet spot. I bet if you made such a graph for 5.56mm it would show 20-24 as the sweet spot.
…Then the response of “no significant gains” past 16" would hold true. Not saying there aren’t any, just that they aren’t significant, especially in the context of a gun intended to be as light as reasonably possible.
-B
It is significant, just not worth the extra length for me.