best barrel length

[shud_b_rite]

Using ggdt I figured out that for my cannon the best barrel length for achieving maximum speed (m/s) is about 200cm. At the moment my barrel is about 70cm with 1.5cm diameter. I can understand why having a longer barrel accelerates a projectile faster than having a short barrel but can someone please explain to me why having a barrel that is too long can slow down or reduce the top speed of the projectile?

[experament-u2]

i think it might just run out of gas and then theres friction

i truly dont know but that might be able ti help

[Insomniac]

If the barrel is too long, 2 things will happen.

1. There will be no gas pushing the projectile foward, and it will be slowed down from friction with the barrel.
2. The projectile will act as a piston and generate a vaccuum behind it, slowing it down even more.

Hope that helps.

[Recruit]

What insomniac said. In a pneumatic the friction from the barrel would slow it down after so long because the expanding gas after so far equalizes with the outside preassure. and if you have a projectile that seal in the barrel well then is will be gin forming a vaccum behind it.