Great feedback, thanks. Let's assume full and detailed case prep, including sorting, neck turning, etc., concentricity verification, and everything else I can do to enhance all elements required for precision. You're right to stress that since without controlling those variables it won't be possible to know if powder changes make an actual improvement.
Given that, my assumption is that certain loads of different powders will complete their burn just as the bullet passes what? The gas port in a semi-auto, or the end of the barrel? CharlieNC suggests using QuickLoad software, which looks like an interesting tool.
I assume that it'd be possible to achieve the same muzzle velocities with a very fast-burning powder that completes its burn early, versus a slower-burning powder that completes its burn at the last possible moment. Would it be a correct assumption that the faster-burning powder would be tougher on the rifling (assuming we stay within acceptable pressure) then the slower powder? So it seems that'd be a point in favor of tuning the powder to the barrel. Are there other factors than muzzle velocity, say, bullet stabilization, etc? I'm hoping you all can give me some things to think about as I tune loads to this longer barrel, and appreciate everyone's feedback so far.
Jeff