what causes shoot up?

[phantomhitman]

I am trying to answer someones question about why mags have shoot up. I am going from what I have read, but I do not know what technical causes it. I know a mech mag is suppose to be chronoed by shooting, holding back the trigger for a second or two, and then shooting again. Why does it need to be chronoed like this and what causes shoot up when shooting a stream of paint? I would like a technical answer (ex-pressure goes here, fills the chamber, etc etc) please. Thanks for you help anyone.

[11 Bravo]

I cant give any technical answer but, I am sure that I have read that it is caused by the valve recharging so fast. The air expands when heated.
I know your probably thinking DUH.

[PumpPlayer]

Higher input pressures cause shoot-up.
Lower input pressure causes shoot-down.

Put it right in the middle (about 850-900 psi) and you'll get consistent shots.

The pressure spike that gives the trigger its reactivity does not fully equalize under high ROF conditions. However, it takes at least 10 BPS to even notice much. The velocity difference isn't going to be more than about 6-8 FPS at any rate unless you're really cranking up the input pressure. The answer's also on AGD's webpage and in the RT manual.

I set my input around 875 psig. I don't get more than a few FPS variation between shots and there's no noticable difference between single fire and rapid.

[athomas]

The retro valves charge so fast that the air in the front chamber becomes hot. The heated air then cools and causes a slight pressure decrease. Normal shooting is slow enough that the air is always cooled when shot. When you rapid fire, the charge and fire sequence is close together so that the chamber air never has a time to cool. As a result, the hotter air stays at a higher pressure and provides more velocity. The effect is called shoot-up. You can simulate this when chronoing by holding the trigger, then releasing and pulling it immediately. The rapid charge and fire sequence doesn't allow the heated air to cool and provides the same velocity effect as rapid firing.

[Maggot6]

Wow, athomas took the words right out of my mouth. As for the CO2 mags, I think it is because all the liquid is shot, and it's the equivalent of 1 shot liquid, to 7 gas, to I would assume it's not 7 times as powerful, but it has to be more...

[Miscue]

Higher input pressures cause shoot-up.
Lower input pressure causes shoot-down.

This is not true... if you take a random marker and change the pressure from high to low... this will not be the case.

The Retro valve is an exception... it's an issue of how it works, not so much high vs low pressure... although yes, the valve's shoot up behavior will change depending on the input pressure.