Fluted Barrels Are Less Accurate...

...as the barrel heats up. The Precision Rifle Blog was recently reviewing the types of barrels used by the top 50 precision rifle champions, including manufacture, length, profile, caliber, etc. The author discovered that of the top 50 champions, only one used a fluted barrel. Looking into the issue further, he observed that Shilen Barrels refuses to flute barrels because it causes uneven expansion when the barrel heats up, adversely impacting accuracy--although Shilen Barrels did not provide research or data. But Accuracy International had performed research on the issue and reached the same conclusion:

Engineers at AI decided to isolate the barrel flutes to see what impact they had on accuracy. The engineers attached a laser to the rifle’s receiver, another to the barrel, and a third to the scope. All three dots were zeroed at the same point, then they started shooting the rifle. They discovered that, no matter which fluted barrel they used, the dots would diverge as the barrel heated. The dots from the devices mounted to the scope and the receiver would stay in place, but the barrel’s device would manifest a point-of-impact (POI) shift. The POI shift from the warming barrel greatly diminished when they used barrels without flutes. 

Engineers determined that the flutes never heated evenly, causing the POI shift. ...

So fluting may be fine for a light-weight hunting rifle--i.e., a "mountain rifle" that is easy to pack around and won't be fired more than once or twice at a given time--but not for a rifle which may be expected to engage in protracted firing strings, such as a tactical rifle.