Energy variations from a rifle, depending on pellet weight
Forums › PCP Airguns › Energy variations from a rifle, depending on pellet weight

Views : 667

October 9, 2018 at 7:35 pm Link
ackuric
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
Matt… I copied and pasted those functions into Excel, but for some reason it didn't work. And got a message saying not enough arguments. How should I modify the functions?
My barrel length is 21". I have no idea what the port size is? Brocock Bantam SniperHR .22.
ackuric
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
Matt... I copied and pasted those functions into Excel, but for some reason it didn't work. And got a message saying not enough arguments. How should I modify the functions?
My barrel length is 21". I have no idea what the port size is? Brocock Bantam SniperHR .22.
October 9, 2018 at 7:51 pm Linkackuric
Glem.Chally
My guess was assuming he's maxing out at 27FPE with the 15.89's. Really just a guess, not knowing which gun or if he's even maxed out etc.
He said hes making 29 fpe, 911 fps = 29.29. So your guess would be off by 2 suggesting he would be around 35? Either way probably pretty close if that is so…JMO
Yes reading fail, thanks
ackuric
Glem.Chally
My guess was assuming he's maxing out at 27FPE with the 15.89's. Really just a guess, not knowing which gun or if he's even maxed out etc.
He said hes making 29 fpe, 911 fps = 29.29. So your guess would be off by 2 suggesting he would be around 35? Either way probably pretty close if that is so...JMO
Yes reading fail, thanksOctober 9, 2018 at 8:58 pm LinkNothing scientific here, just guessing 😁:
1) 15.9 ~ 911 fps – 29.3 FPE
2) 18.1 ~ 872 fps – 30.48 FPE
3) 21.14 ~ 825 fps – 31.96 FPE
4) 25.39 ~ 780 fps – 34.31 FPE
Please get a chrony and verify.
Nothing scientific here, just guessing 😁:
1) 15.9 ~ 911 fps  29.3 FPE
2) 18.1 ~ 872 fps  30.48 FPE
3) 21.14 ~ 825 fps  31.96 FPE
4) 25.39 ~ 780 fps  34.31 FPE
Please get a chrony and verify.
October 9, 2018 at 9:13 pm LinkE=MC2 is a basic yes, but understandable and accurate enough, that's why I posted it. It's close enough to help people understand light pellets vs. heavy pellets from the moment they leave the muzzle. I understand it's a lot more complex than that if you include internal ballistics, which is part of what you cut and pasted, but way beyond the scope of this question. For his question, all you really need is muzzle velocity and pellet weight.
E=MC2 is a basic yes, but understandable and accurate enough, that's why I posted it. It's close enough to help people understand light pellets vs. heavy pellets from the moment they leave the muzzle. I understand it's a lot more complex than that if you include internal ballistics, which is part of what you cut and pasted, but way beyond the scope of this question. For his question, all you really need is muzzle velocity and pellet weight.
October 10, 2018 at 12:24 am LinkApples to oranges but I think it matters on what you are shooting, Pesting.
example , I got a 177 Vulcan shooting 10.34 Gr JSB Domed at 962 FPS
I have been sampling the 8.26 wad cutters, Never did I ever think I would be shooting euro doves with this light pellet, But the wad cutters do massive damage , compared to the heavy dome pellets ,
Just FYI if your hunting in 48 yards and you need a little more knock down, check out the wad cutters , I may check into the 22 and 25s and see what they offer.
Mike
Apples to oranges but I think it matters on what you are shooting, Pesting.
example , I got a 177 Vulcan shooting 10.34 Gr JSB Domed at 962 FPS
I have been sampling the 8.26 wad cutters, Never did I ever think I would be shooting euro doves with this light pellet, But the wad cutters do massive damage , compared to the heavy dome pellets ,
Just FYI if your hunting in 48 yards and you need a little more knock down, check out the wad cutters , I may check into the 22 and 25s and see what they offer.
Mike
January 1, 2020 at 4:44 pm LinkWhile throwing all this math around is fun. It is pure speculation unless proven velocity differences can be established with a Chrony.
Reason being, the gas check on different brands of pellets can make a significant difference in the result calculated. Another factor to consider is rate of twist and barrel length, for obvious reasons.
The only true way to know is to shoot 510 shots with one pellet through a chrony. Refill and repeat with the other pellet.
That being said one could create a pretty accurate expectation if he/she had the same gun, same settings, and the same pellets as the person providing the data for comparison.
Now that I have thought about this I wonder if it would be of any use to anyone if I posted it? Or if these thoughts should just remain in my head? 😂😂
Either way, thanks to the people that contributed to this topic.
While throwing all this math around is fun. It is pure speculation unless proven velocity differences can be established with a Chrony.
Reason being, the gas check on different brands of pellets can make a significant difference in the result calculated. Another factor to consider is rate of twist and barrel length, for obvious reasons.
The only true way to know is to shoot 510 shots with one pellet through a chrony. Refill and repeat with the other pellet.
That being said one could create a pretty accurate expectation if he/she had the same gun, same settings, and the same pellets as the person providing the data for comparison.
Now that I have thought about this I wonder if it would be of any use to anyone if I posted it? Or if these thoughts should just remain in my head? 😂😂
Either way, thanks to the people that contributed to this topic.
January 1, 2020 at 5:06 pm LinkI think we have some pretty smart people posting to this thread even if it’s hard to understand the math, lol.
Thank You all for the contribution and Happy New Year!
I think we have some pretty smart people posting to this thread even if it’s hard to understand the math, lol.
Thank You all for the contribution and Happy New Year!

Author
You must be logged in to reply to this topic.