Alecto longer barrels

[Taylor]

Wouldn't that be negated a bit by the fact that the pressure of the air will be lower in a longer barrel as the pellet reaches the muzzle end?

Eventually, yes. There is a point where increasing barrel length swings the opposite way and causes a decrease in velocity.

It’s also a myth a longer barrel automatically means better accuracy. It doesn’t.

Further explanations here
http://airgun-academy.pyramydair.com...barrel-length/
http://www.pyramydair.com/blog/2005/...important.html
http://www.pyramydair.com/blog/2007/...locity-in.html