Ah the good O'L bore size question, I was recently wrestling with this. I'm currently building a custom length VSR-X with Careful and I chose to go with a 6.05mm inner diameter. Why? Simply because I'm lazy and don't want to break down the rifle regularly to clean the barrel. The issue I have with a 6.01 or tighter inner diameter is that if you don't keep it super clean, it can lead to jamming, especially if your using low quality BBs.
The fact of the matter is that we have no major scientific side by side comparisons to go off of. It's pretty much speculation BUT the longest shots have been made with extremely tight bore barrels. I would say that tighter is better, but it comes at the cost of high maintenance & potential jamming with low quality BBs.
I would recommend avoiding a wide bore battle like orga, I believe the "air cushion" is just a good marketing gimmick.
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