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Originally Posted by Primus
Let's get you thinking a little more Carl  With all that said what do you suspect happens (or not) when you upgrade the bits in the mechbox (stronger spring, spring guide, etc). Will these affect/distort the ratio of the cylinder port/barrel lenght?
What I'm getting at is if I upgrade basically everything in the mechbox should I be looking at a cylinder with different porting or is this not affected at all? |
I would guess that a stiffer spring would change ideal matched cylinder.
My reasoning is that an upgrade which results in a higer final bb velocity with the same length barrel would have to apply a higher acceleration rate to the bb. This would require a higher pressure. Actually more like a pressure profile as the pressure probably varies throughout the bb travel.
A higher pressure profile would mean that they cylinder air would compress to a smaller volume and you'd have a higher leak rate around the pellet, nozzle, and nozzle-hop up junction. So if you previously had a perfectly matched cylinder and then you upgraded the spring, you'd have a short cylinder.
However, it's hard to say if you'd actually get barrel suck. Barrel suck is a pretty simple phenomenon if you think of it.
If the:
(cylinder volume - leakage losses) < barrel length
then you don't push enough air to get the bb out the barrel and the bb at some point starts to decellerate in the barrel as it pulls the air below 1atm.
However if the cyl' volume is significantly higher than the barrel volume and the piston head hits the cylinder before the bb leaves it doesn't necessarily mean you get barrel suck. The air pressure behind the bb is still higher than 1atm until the pellet runs down the barrel for awhile. If the pellet leaves just as the volume behind the pellet matches the cylinder volume (plus leakages) then you actually have ideal efficiency.
The actual piston and bb trip times are probably so fast that the idea that the piston would be pulled back by the mechbox before the pellet leaves probably doesn't happen.
Consider an AEG ROF of 900spm ~15shots per sec (0.067sec/shot)
If said AEG shoots at 330fps with a 340mm barrel (1.13')
assume average speed of 165fps (0 at beginning, 330 at end). This implies constant acceleration which is probably not the case, but probably not a bad approximation.
barrel trip time: 1.13ft/165ft/s = 0.00685sec
0.00685sec <<< 0.067/2 (0.0335sec)
I divide the piston cycle time in half because by the time the piston hits the cyl, half the motion cycle has passed. In one more half cycle, they piston will be withdrawn. However this is generous as the piston moves forwards a lot faster than it moves back which means I should allow more time for the sector to come around.