Question about changes in Pump Gun FPS

[Webmaster]

Here is something that surprises me:

Take a pump gun - like a Sniper 2.

Hold the pump forward and shoot, chrono the shot. (shot A)

Dont hold the pump forward, shoot, allowing the bolt to spring back a bit from the shot, chrono the shot. (shot B)

In my experiance, shot B is actually a higher FPS than shot A.

Why is this? You would think with the tight seal and with the air not wasting energy to push the bolt back, that shot A woud have a high FPS.

So - um - why is this?

[Gecko]

thats weird.....
if i don't hold the pump forward i lose about 15 fps....
what kind of guts are you running?
i have a evolution bolt, with a stock valve sprung with whatever i found at the bottom of my toolbox.
Gecko

[thei3ug]

By any stretch of the imagination, all things equal, it is impossible.

By allowing you bolt to stray you should be occluding the valve exhaust. The only thing I could say is... maybe your bolt wasn't manufactured quite right.

In my experience Worr games has incredible tolerance swings. It's quite possible things are just a tad off.

[Redkey]

if you shoot 20 shots and calculate the average the velocity for each method?

[Webmaster]

well - I am going to test this again and write them all down when i go out again - Im telling you - it doesnt make sense - but it IS what I have observed in the past.

[shortfri]

this sounds crazy but it has to do with the springs behind the bolt keeping pressure on valve. i know nothing about your marker, but i played stock for a long time in the late 80's and early 90's and my pump did the same thing. with my pump when it was open like you said there was more pressure on the valve pin seat that let more air come out as you shot. i know this sound crazy but when we noticed the problem we cronoed all types of markers and they all did the same thing execpt one and i'm not sure what it was, and this one marker could have been a fluke.

[ShinyGuy]

Makes perfect sense in a nelson gun. The bolt moves back and increases the tension in the mainspring holding the valve open longer.... But it sounds like you're talking about a sheriden which I would expect to do the opposite. So ... basically I have no clue:confused:

[rhetor22]

this is way out there, and would not be true because of the pressure required to increase the actual fps, BUT:

maybe when the bolt springs back, it bounces forward increasing the pressure slighty AFTER the ball has started moving. This way that pressure is not used to overcome the initial friction and the "objects at rest remain at rest" thingy.

could just be extreme coincidence.