Originally Posted by aa1911
.22 LR for example, after about 17", any extra barrel length is completely unnecessary; hence the 'bloop tube' on small bore target rifles. A standard velocity round gains nothing past that 17" (approx) mark but you do benefit from a longer sight radius.
Where did you get 17" inches from? The writer of Gunblast did a little testing with a Ruger 10/22 Carbine, and a Ruger Charger (10" pistol with 10/22 action) using high velocity Federal hollow point, he chrono'd "1203 feet-per-second (fps) from the sixteen inch barrel, but still averaged 1163.9 fps from the ten inch Charger barrel." Barely 44 fps from a 10" barrel to 16". Chronos from even smaller handguns still exceed 1000 fps, just shy of what a rifle barrel would produce.
I think what makes a longer barrelled gun "more accurate" is that it is easier to hold steady and hit your target. Like a snub nose revolver vs. a full size service pistol, or a small lightweight carbine vs. a heavy rifle. They might be equal when on a vice, or bench, but when shooting off hand you'll see the merits of the larger weapons. If barrel length had no effect on performance, what was the reason for the big bulky near-30" barrel muskets, Mosins, and M1 Garands? While there may be subtle differences in accuracy between a 16", 20", or even a 24" bull barrel, I think you know which would be the easiest and most predictable to hit your mark.