Thanks! I think I got itThis Data is for an AEG. 550mm is too long. If you do not understand, get around the 400mm mark as this is a pretty good all round length.
after I play around with new cylinder I found that too much air or bad Barrel ratio will make 'sharper' pop sound(not sure if that effect accuracy or not),
kinda similar to real firearm with a short barrel when gunpowder burned outside a barrel and produce louder sound and bigger fireball
and if 'The longer the inner barrel the quieter' and 'too long barrel will make an airsoft inaccurate' maybe it possible to make a longer barrel without affecting an accuracy?