Re: Barrel length vs. Accuracy
Good points. I conjecture that this could be carried for other steps.
If you're shooting with a scope and Std Velocity ammo, the 16"-17" bore length is probably optimal.
But the peak velocity may or not be the best attribute of a given load.
Going with a longer barrel might result in a lower velocity, and this might better ensure the round stayed subsonic beyond the muzzle.
Adding more bore length again might even make more brands of ammunition eleigible for subsonic performance. (i.e 'shoots nice, but it's just too marginally fast..., etc.').
If you're using subsonic and irons, a larger bore unrifled extension (commonly called a 'bloop tube' after the sound effect it adds) can be employed to extend the sight radius.
Overall sight radius length should be figured to adjust sight click increments precisely to common (i.e.1/2MOA or 1/4MOA, etc.) POI change increments at the intended distances.
Typically, a shorter barrel is comparatively stiffer, and should reduce harmonic swing; but in practice, some bets just never pay off as expected.
Greg