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PostPosted: Thu Feb 22, 2018 3:54 pm 
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Joined: Mon Feb 06, 2017 8:13 am
Posts: 156
Is there any way to calculate what kind of potential FPE an Airguns is capable of at a given psi if you know what energy it shoots at a lower psi?

If an airgun regulated at 800 psi shoots 9fpe, is there a way to “guess” what it might shoot at say 1200 psi? I understand that it’s complicated (valve/hammer springs, transfer port limitations, etc), but assuming the hammer spring is capable of dumping enough air at the higher pressure...


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PostPosted: Thu Feb 22, 2018 3:56 pm 
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enjoy

http://closefocusresearch.com/calculati ... un-systems

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PostPosted: Thu Feb 22, 2018 3:59 pm 
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Easier just to data log. Record the PSI, # of shots and the FPS. Than seat of the pants Chrony.

Depends on the cal, the pellet, barrel length, condition of the seals. Plus everything else you said.


Last edited by leadslinger on Thu Feb 22, 2018 4:02 pm, edited 1 time in total.

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PostPosted: Thu Feb 22, 2018 4:00 pm 
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leadslinger wrote:
Easier just to data log. Record the PSI, # of shots and the FPS.


agreed

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PostPosted: Thu Feb 22, 2018 6:28 pm 
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Location: Coalmont BC
There is a direct relationship of the POTENTIAL maximum FPE to pressure.... In fact the maximum possible is the product of the pressure (in psi) x the bore area (in sq.in) x the barrel length (in feet).... because of the following relationships....

Energy (FPE) = Distance (ft) x Force (lbs) .... (hence the meaning of ft.lbs of energy)

Distance (ft) = Barrel Length (in) / 12

Force (lbs) = Pressure (psi) x Bore Area (sq.in)

therefore the Maximum Possible Energy (FPE) = Pressure (psi) x Bore Area (sq.in) x Barrel Length (in) / 12

Note that this would require 100% efficiency, and the result would include the energy imparted to the air exiting the muzzle as well as the bullet.... It also requires constant pressure throughout the time the bullet is in the barrel (which would require an infinitely large air reservoir and the valve being open until after the bullet exits the muzzle).... Because of these, the very best PCPs have huge difficulty managing to reach even 50% of the maximum theoretical FPE.... so if you want a practical formula that can estimate a "lofty goal" for a PCP, you can change the divisor to 24 instead of 12 in the above formula.... Most PCPs operate at less than 50% of that lofty goal, because the ports restrict the airflow, and/or the valve restricts the dwell.... so you will understand that they are only delivering a fraction of what is possible....

Having said that, if a gun is tuned to the maximum possible FPE at the pressure you are using (ie loud and inefficient), and you increase the pressure by 50%, the FPE should also increase by 50%.... However, this will depend on having enough hammer strike to be able to fully open the valve at the new, higher pressure.... and keep it open until the bullet exits the muzzle.... just like it would have been doing (at maximum) at the lower pressure.... It is quite likely, however, that if you increase the pressure and make no other changes, the gun may actually shoot slower, because you need more hammer strike to open the valve against that greater pressure....

Bob

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PostPosted: Thu Feb 22, 2018 7:18 pm 
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Now that's what I call an intelligent, well thought out answer, to a member's question!

Thanks for sharing Bob! Excellent.

Avianmanor

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PostPosted: Fri Feb 23, 2018 10:16 pm 
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Bob layin’ it down. Thanks!


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