I have never been one to subscribe too much to the barrel length debate. I do know that through my shooting I generally keep my .308 equipped with a 20in barrel and my .223/556 barrels vary from 14.5in to 20in, depending on the application. While I understand that there is velocity loss though less gas expansion, I tend to look more at the repeatably of the shot. Is the barrel consistent enough to accurately put rounds down range as close together as possible?

You can change or even eliminate muzzle flash, muzzle blast and other things with cartridge building, muzzle devices and suppressors. With accuracy you are limited to the barrel harmonics and loading rounds that will induce consistent harmonics and barrel whip.

This article takes a look at different 5.56 cartridges and how barrel length can change velocity, accuracy and lethality while also decreasing weapon function.