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Stalker, I get what you're saying and would tend to agree...but a question or two spring to mind.
Isn't the traveling speed of the piston a direct factor in resulting FPS as well?
Don't the ports serve more purpose other than to break the airseal and fill the cylinder with "fresh air" quickly on the piston head's return stroke?
When the spring is fully compressed, the piston is at it's most rearward position. In a full cylinder, it's still in the compression zone (i.e. if it moves forward, it'll start forcing air and start building up pressure behind the bb). In a ported cylinder (port mid-way, 3/4 back etc...) the piston isn't in the compression zone yet and has some distance (maybe half the cylinder, maybe less...) to travel before it starts moving air.
I'm not a big physics guy...like you I'm more of a learn with hands/eyeballs type...so I'm probably going to butcher this explanation...
If a piston is at rest and starts to move forward, the pressure builds behind the bb and eventually reaches a point where it starts to move the bb past the hopup nub. As it continues to move forward, the piston speed will increase to hit a max speed largely based, I'd figure, on the expansion/compression characteristics of the spring/coils/material/temper. Perhaps the acceleration curve is steep...maybe more linear.
Now, if it's a full cylinder, the piston will start the bb moving before the piston has reached full speed...and in a very short barrel the bb could very well exit the barrel before gaining the full compression benifits that the spring could provide...resulting in a lower than optimal velocity.
In a ported cylinder...the piston has time to reach a higher speed before starting to compress the air in the compression zone. So the pressure behind the bb is higher than that of the same setup but with a full cylinder...resulting in a relatively higher FPS.
Taken to an extreme...where the port is very much forward...so that the piston is traveling as fast as it can...but the compressible air volume is tiny...you'd end up with a very low FPS because the volume of air in the compression zone may not exceed the volume within the inner barrel.
I hope I explained things right...I probably didn't.
I'd appreciate your opinion,
Tys
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