It's 'way too early to give you any great amount of field results, Steve, but my latest pet rifle has a three-groove barrel on the basis of the logic on their side. (Plus the fact that a top bench-rest barrel-maker recommended it.)
First, why not? I have no answer to this question.
Second, the barrel-makers' rule of thumb devotes 25% of the bore's circumference to lands, 75% to grooves. This means that in a three-groove barrel, the lands and grooves are twice as wide as they'd be in a six-groove barrel of the same caliber. In the .224 barrel on my .220 Howell, the three lands are not very wide. They'd be awfully narrow in a six-groove .224 barrel.
Also, the fewer lands there are, the fewer also are (a) the sharp edges cutting into the bullet jacket and (b) the "gutter" angles at the bottoms of the grooves where fouling is hardest to remove.
So much for rationale. Results later -- but I'm quite confident with this rationale and expect good results.
