I don't think there is any question in my mind that longer barrels yield higher velocities, but I would bet that using faster powders in the shorter barrels could narrow the gap because you are still burning powder after the bullet has left the barrel (rifle cartridge in a 13 inch barrel).
As far as the accuracy results, I'm seeing that the accuracy reported is affected by different bullet weights and powders with many of the tests showing the accuracy flip flopping on the chart. It just shows me that certain barrel lengths and twists react differently to a given cartridge. Perhaps more time spent on working up the most accurate load for a certain barrel combination would be a better comparison.
I think most of us would agree that one firearm likes certain loads better than another firearm.
All content of this site is copyright 2003 - 2017 AR-10(T)™, AR-10™, are trademarks of ArmaLite, Inc.® AR10T.com is NOT endorsed or affiliated with ArmaLite, Inc.®
About AR10T.com
AR-10(T) is a community focused on rifles, optics, scopes, gear, accessories, and components used by the professional operator and skilled marksman. Enthusiasts, shooters, and gunsmiths alike contribute to our gallery, articles, and reviews Thank you for visiting!