I've used all sorts of barrels over the years, I've gone through bore sizes and different lengths and I still go back to my old armson barrel that I've used since '94.
it's big and every paint drops straight through .
I think bore size will help with consistency over the chrono, but that's about it.
I used to put a wind measuring device on a stick about the size of a pot lid about 20 metres away and the same bit slightly further away but further left and one further right, then a set of goggles behind a bucket so I could see half the goggles, then I'd fire at the wind bits and make them spin , then shift to the left then to the right and then fire at the goggles, when I'd got evrything spinning and the goggles hit then I would kneel and do the same thing, then I'd move up and down and do the same thing, I'd do this everyday ( I used to work at a paintball site and repair the rental guns during the week)
People used to say that I got them out with lucky shots, or how did I hit the end of their barrel,
shooting , shooting, shooting is what I did, you won't hit the target every single time, as paint is not that accurate, but 9 times out of 10 I would.
That's how you get accurate.
My team still takes the piss out of me for my armson, and recently I've started using a carbon barrel with inserts, but I don't rate it as much as my armson barrel.
so when someone tells you that their barrel will make you more accurate, it's true, but only if you practice with it, and not just a hopper everynow and then, but a box , everyday for months, then you'll see your accuracy improve.