FPS goes up before coming down

Hi fellow Airforce Addicts,

So from 200 bar my Talon is giving me a nice flat fps curve with rubber Oring behind tophat but for first dozen shots or so it actually creeps up in fps by a few pounds per shot, before very slowly going down.

So my question is why would it climb before going down?? – when the tank pressure is steadily depleting from the 1st shot?? What does it indicate? I’m guessing it means I’ve insufficient hammer spring preload but you guys will know.

Tony if you read this, I think I need one of your curvy Talon anti slap brass hammers, as the one I have is scraping the inside of the gun (not being one of yours I hasten to add!)

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Viewing 3 replies - 1 through 3 (of 3 total)

chrisyboy

Participant

April 11, 2015 at 10:30 pm

Thanks guys. Really helpful. There is so much to learn with Airforce guns, but that’s the juice for me. :fishinghole:

Anonymous

Inactive

April 11, 2015 at 4:32 pm

Strange, my Condor SS 25 cal has 2 small pecks in the middle of the shot curve.
It shoots a sub 1″ ctc group at 100 yards though.

The shot string had two peaks at 920fps,
@2800psi started at 896fps and slow climbed to 920fps 14 shot later
@2550psi dropping to 894fps 13 shots later
@2350psi slow climbed again to 921fps 13 shots later
@2100psi dropping to 897fps.
For a total of 40 shots, from 897- 921fps that is and extreme spread of 24fps.

~ GKU

genet

Participant

April 11, 2015 at 12:22 pm

It indicates that your gun is functioning normally. Simplifying a little bit, there are two big forces acting on your valve – the force of the hammer knocking it open and the force of the pressure in the tank, which tries to push it closed. At your highest pressures the tank is forced closed more quickly, so as tank pressure drops it’s allowed to stay open longer and longer, resulting in higher and higher velocities. Eventually, you reach a point of equilibrium (your peak velocity shot) where the pressures are about perfectly balanced. After that things start to behave the way you imagine – declining with each shot as tank pressure goes down.

GsT

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