So researching this topic it seems to yield mixed results some say for any long range weapon you should be using 6.01 or smaller inner diameter barrels and others say it really doesn't matter and its just about barrel quality and a small group state that 6.08 barrels are the way to go and interestingly PDI actually recommend this size for longer range weapons.
No doubt about it barrel quality is the most important aspect of a barrel but I wondered what difference the different inner diameter sizes actually made. When I first thought about this problem my thinking was that you would want a barrel with the smallest size inner diameter because this would mean that the BB will be kept as straight as possible where as something wider would actually allow the BB to move around and the only thing a larger inner diameter would be good for is reducing your FPS.
More research into this I think that it might just be the other way around with a smaller inner diameter the BB will be hitting the sides of the inner barrel which will cause the spin of the BB to be reduced slightly and that resulting in less range and accuracy. Where as the 6.08 gas will create a cushion around the BB which will mean that the BB never touches the sides of the barrel.
That's the theory anyway if this is actually true I don't know but I want to find out. I have two 455MM PDI inner barrels one which is 6.03 and another which is 6.08 and I plan to test both to see which one will offer the best range and accuracy. I am still trying to figure out the best way of testing this as I don't have access to any large areas indoor or out so my only real way of testing would just be to use the gun for the day and watch the scope cam footage back and see what the accuracy was like that way.
I wondered though what others thought about this and which size barrel is thought to offer the highest accuracy?