Re: 300 win mag???
One of the main benefits to the larger case capacity is that you can actually fill it up with enough slow burning powder to do some good velocity wise. You can not take advantage of this without having enough barrel length. While you can get away with shorter, and it appears Tac-Ops does, I think the best results for a hand-loader are going to come with the 26" barrel.
As to the Tac-Op study:
I don't truly know how you can take 4" and not either lose or gain velocity?? I definately don't want to argue with Tac-Ops as they make a hell of a rifle, but that seem contrary to anything I have ever heard or seen. I know people are getting good result with 18" in the .308, but they aren't pretending there is absolutely no velocity gain when moving the barrel up a couple inches either... I wonder if they mean they don't see a 'detrimental' lose in velocity until 22". I guess I need to do my own study...
Dave