The key factor is the space between the bb and the barrel. The more contact the BB makes with the barrel as it goes through it the more disruption there is to the hop-up. Therefore the tighter you go, eventually, the benefits of a tighter barrel become overshadowed by the downside of having too much disruption to the BB's backspin. There is a plus side though, the less space between the barrel and the BB the better seal the BB makes against the barrel and thus more efficiently turns the pressure behind it into BB exit velocity.
It is also important to use the correct size of BB for your barrel. It may not be to commonly known but different brands and batches of BBs have significantly different sizes of BBs. from 'large' 5.96-5.98mm diameter, to 'small' 5.90mm diameter or even less. For example let's have a look at these three brands of BBs; KSC 'perfect' 0.20g, Tokyo Marui's 0.20g BBs, Excel's 0.20g BB, a Chinese Brand called 'Goldenball' 0.20g, and lastly the new-on-the-market Madbull match grade 0.20g BBs. 15 of each were taken and measured precisely with a vernier caliper, then the average was calculated.
http://www.redwolfairsoft.com/redwolf/a ... ulletID=73
bizarre ça me rappelle quelque chose sauf que ce n'était pas sur 0.20
)
.