Take a look at the Un1tec barrel from lucky.
Its a straight bore barrel kit so it doesnt have a step in the bore, this reduces barrel breaks and means that it shoots through better and makes your gun quieter.
The way it screws together means it can never be misaligned. Plus If you change markers, its only £10 for a new back.
Its the lightest aluminum barrel out.
Bores range from .685 to .696. (.689 or .693 is the best size for most paints)
It got
10 out of 10 on pbreview
And its a little cheaper than the CP....