What does barrell length have to do with accuracy

[jerkface11]

Seems to me that a longer barrel provides for a complete burning of the powder

Even a 2" barrel has burned all the powder that's going to burn.

 

[btg3]

The effect of barrel length on accuracy is different than the effect on precision... because accuracy and precision are not the same thing.

http://celebrating200years.noaa.gov/magazine/tct/tct_side1.html

 

[The Lone Haranguer]

Put in a machine rest, the groupings will be very close to the same, varying more between makes and models of guns, and even individual examples of the same kind of gun, than by barrel length. What the longer barrel does is help make the shooter more accurate. The closer the sights are together (the sight radius), the more a small variation or error in sight alignment will disperse the shots.

 

[mljdeckard]

Proportionally the barrel on a tank gun is very short, and it is quite accurate for thousands of yards.