After market barrel length question

[KDX]

I was thinking of building a 10/22 and saw that Green Mountain has 16, 18 and 20 inch replacement barrels. I remember reading somewhere that a .22cal bullet reaches optimum velocity at 16 or 16.5 inches. What is the advantage of going to a longer barrel?

 

[Armament]

Primarily Stability. The extra weight and length makes a big difference.

 

[m39a2]

For Iron sights it increases the sight radius as well.
Scott