Generally speaking, assuming all variables are kept the same (chamber, crown, bore diameter, ect), a heavy barrel will shoot more accuratly. This is because of barrel harmonics. Each time you shoot, although you many not realize it, the barrel vibrates. And even very large bull barrels vibrate. But what the bull barrel does, is it has more control over the vibtrations of the barrel, and the vibrations are kept more consistant.
With a skinnier barrel, there are more vibrations and these vibrations can be less consistant, hence, making the gun less accurate.
This is also why barrel tuners are used; to limit and control the ammount of vibrations a gun has.
Cutting a barrel down in lenght isn't going to affect accuracy at all, the only thing it may do is that when you go to recrown it, you may be getting a better crown.
Usually, benchrest guys who use a tuner like the longer barrels, and guys without tuners it doesn't seem to matter.
The only real advantage a barrel over 16" has is its better on the bench (more weight).
Hope this helps,
Jordan
