Cylinder vs Barrel Length

[Johndabomb]

After reading on a lot on Airsoft forums about barrel length vs cylinder size I am non the wiser. I have an SRC M16A3 and it has a ported cylinder with a 509mm length barrel but what I've read is that if a barrel is longer than 450mm is should not be ported, completely sealed. Would a completely sealed cylinder for my m16 increase the gun's fps? And why would SRC port a cylinder if it isn't needed or useful? Someone please explain.

[TPI]

From what i just learned from Mr Black they may have done it to decrease fps and make it site friendly.

[Deva]

What's your current fps? I doubt it's anything to be concerned about.