Toss this in excel and change the pellet weight (15.89) around...the (.0145/.22) is a port reduction correction factor, put your port size there...the (19.5/24) = barrel length so replace 19.5 with barrel length, the 1900 is avg pressure at valve seat...the *.90 Correction factor in equation is for pellet mass to air mass ratio, the number would go UP the heavier the pellet, and down the lighter...I did not go to that length in this example I left the ratio the same.
=ROUNDDOWN(SQRT((ROUNDDOWN(((15.83*2)+ROUNDDOWN((0.22^2 * 3.14159/4) * 1850 * (19.5 / 24) * 0.13/0.22,3))/2,2)*450240)*0.85/15.83))
the example above gives me 915 FPS with 15.89. Which is 29.5 FPE
=ROUNDDOWN(SQRT((ROUNDDOWN(((18.13*2)+ROUNDDOWN((0.22^2 * 3.14159/4) * 1850 * (19.5 / 24) * 0.13/0.22,3))/2,2)*450240)*0.9/18.13))
If I change the pellet weight ONLY to 18.13 I get 884 FPS. Which is 31 FPE. Roughly 2 FPE Gain.
=ROUNDDOWN(SQRT((ROUNDDOWN(((25.4*2)+ROUNDDOWN((0.22^2 * 3.14159/4) * 1850 * (19.5 / 24) * 0.13/0.22,3))/2,2)*450240)*0.9/25.4))
If I change the weight to 25.4 I get 821 FPS @ 38 FPE 9 FPE Gain over 15.89
Those numbers will likely change once you put in your actual numbers (port size/barrel length/pressure)
The above formula requires one additional correction factor that I use to be more accurate but its a pain in the butt to implement so I will leave it out...the above will give you a really close idea of what happens with pellet weight changes...but the lighter you go on pellet the less likely you will reach that number due to the lack of my additional Correction Factor...also the pellet to weight ratio factor changes with each weight which I did NOT provide in this example because I am too lazy to do the math and don't even know the mass of air you use per shot based on your volumetric efficiency...
Typically what happens with lighter pellets, the lighter you go the less of the Pressure Gradient applies to them due to their acceleration...the heavier pellets both move slower so have more KE transfered to them on TOP of having a higher pellet/air weight ratio...hope that makes sense.
-Matt
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