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 Posted: Wed Jan 20, 2010 2:47 pm |
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| Slavia |
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| Quote: |
| Initially, I would think both calibers would encounter the same pressure, but as soon as the pellets start to move, the .22 would reduce pressure faster due to the size of the barrel. |
I agree about the greater volume after the pellet starts to move, but how about detonation at that moment of peak pressure? It strikes me that the stress on the spring and the risk of detonation would be the same at that moment, and yet nobody worries about damage in this case. |
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| Posted: Wed Jan 20, 2010 3:08 pm |
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| Lipoly |
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| Slavia wrote: |
| Quote: |
| Initially, I would think both calibers would encounter the same pressure, but as soon as the pellets start to move, the .22 would reduce pressure faster due to the size of the barrel. |
I agree about the greater volume after the pellet starts to move, but how about detonation at that moment of peak pressure? It strikes me that the stress on the spring and the risk of detonation would be the same at that moment, and yet nobody worries about damage in this case. |
Given that larger caliber pellets travel slower, thus being in the barrel longer, thus presumably keeping a higher PSI, it seems that maybe the two factors would balance out, and the pressure would be the same regardless of caliber.
My point being that I agree w/Slavia. If an air rifle can handle a .22 caliber at some pellet weight, it seems it should be able to handle the same weight at .177 caliber. The internal pressure (and thus the chance of dieseling) should be the same.
Of course, this should work in reverse then. If a .177 can shoot a 5.4gr PBA Raptor w/o damage, shouldn't it be able to shoot a .22 @ the same (insanely low) weight w/o damage? |
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Philip
RWS 350 .22 w/Leapers 4-16x50
Crossman 1377 |
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| Posted: Wed Jan 20, 2010 5:18 pm |
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| rsterne |
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I guess this boils down to whether or not the pressure available is sufficient to start the pellet moving before the "combustion event" (or detonation in the worst case) takes place.... Bear with me here while I type as I think (always dangerous)....
If the combustion / detonation occurs and the pressure peaks before the pellet starts to move..... what possible difference could it make what the pellet weighs?.... As far as the chamber and spring are concerned, the barrel may as well be welded shut at the breech end, completely blocking the transfer port, correct?....
For heavy pellets to cause more of a problem than lighter ones.... the pellet MUST be starting to move before the combustion pressure goes so high that detonation occurs.... Otherwise, the pressure peak (and type of combustion) would be the same.... Assuming this is the case (and it MUST be or heavy pellets could not possibly influence the pressure created).... then the pressure must be peaking after the pellet has started to move but before it exits the barrel, also correct?....
For all the arguments made in this post that heavy pellets could cause damage, while lighter ones don't, to be valid.... we will now assume that the pellet must be starting to move before the pressure peaks.... Now we can look at the difference between different calibers.... First of all, two identically shaped pellets will have a weight proportional to the cube of the difference in the diameter.... A .22 cal pellet is 0.216" in diameter.... which means it is 0.216 / 0.177 = 1.22 times as big as a .177 pellet.... That means it should be 1.22 x 1.22 x 1.22 = 1.816 times as heavy.... Taking a 7.9 gr. pellet in .177 x 1.816, that gives us a 14.3 gr. pellet in .22 cal.... Hey, how about that, it works!....
So a .22 pellet is ~82% heavier than an identical .177 pellet.... so why doesn't every Springer detonate in .22 cal?.... Well, the base area of the pellet goes up by the square of the diameter.... or 1.22 x 1.22 = 1.488 times.... Since the force the air pressure can exert on the pellet equals the pressure times the area.... the air pressure exerts ~49% more force on a .22 pellet than on a .177 pellet.... To compare a .22 pellet to a .177 pellet, we would have to compare it to one that is 1.22 times as heavy.... ie instead of 7.9 gr. that would be 7.9 x 1.22 = 9.6 grains.... In other words, a 14.3 gr. pellet in .22 cal would act like a 9.6 gr. pellet in .177 cal in terms of how much air pressure it takes to start it to move and how it will accelerate (initially) down the barrel....
Want to double check these figures to see if they make sense in the real world?.... Take a .22 Springer that launches a 14.3 gr. pellet at 700 fps.... What velocity should be expect in .177 cal?.... Roughly 700 x 1.22 = 854 fps with a 7.9 gr.... Sure sounds about right from my experience.... 
Incidently.... If we look at the FPE developed by the Springer in the example above.... we get 15.6 FPE in .22 cal and just 12.8 FPE in .177 cal.... ie the .22 cal has 1.22 times the energy.... How about momentum?.... In .22 cal we get 0.0446 compared with 0.0300 in .177 cal.... with the .22 cal coming in at 1.488 times the momentum.... Note that all these numbers work right back to their relationship to the difference in the bore.... and yet also agree with most Springers in the real world.... 
Bob |
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Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal: Too many to count! |
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| Posted: Wed Jan 20, 2010 10:36 pm |
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| sniper |
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| rsterne wrote: |
I guess this boils down to whether or not the pressure available is sufficient to start the pellet moving before the "combustion event" (or detonation in the worst case) takes place.... Bear with me here while I type as I think (always dangerous)....
If the combustion / detonation occurs and the pressure peaks before the pellet starts to move..... what possible difference could it make what the pellet weighs?.... As far as the chamber and spring are concerned, the barrel may as well be welded shut at the breech end, completely blocking the transfer port, correct?....
For heavy pellets to cause more of a problem than lighter ones.... the pellet MUST be starting to move before the combustion pressure goes so high that detonation occurs.... Otherwise, the pressure peak (and type of combustion) would be the same.... Assuming this is the case (and it MUST be or heavy pellets could not possibly influence the pressure created).... then the pressure must be peaking after the pellet has started to move but before it exits the barrel, also correct?....
For all the arguments made in this post that heavy pellets could cause damage, while lighter ones don't, to be valid.... we will now assume that the pellet must be starting to move before the pressure peaks.... Now we can look at the difference between different calibers.... First of all, two identically shaped pellets will have a weight proportional to the cube of the difference in the diameter.... A .22 cal pellet is 0.216" in diameter.... which means it is 0.216 / 0.177 = 1.22 times as big as a .177 pellet.... That means it should be 1.22 x 1.22 x 1.22 = 1.816 times as heavy.... Taking a 7.9 gr. pellet in .177 x 1.816, that gives us a 14.3 gr. pellet in .22 cal.... Hey, how about that, it works!....
So a .22 pellet is ~82% heavier than an identical .177 pellet.... so why doesn't every Springer detonate in .22 cal?.... Well, the base area of the pellet goes up by the square of the diameter.... or 1.22 x 1.22 = 1.488 times.... Since the force the air pressure can exert on the pellet equals the pressure times the area.... the air pressure exerts ~49% more force on a .22 pellet than on a .177 pellet.... To compare a .22 pellet to a .177 pellet, we would have to compare it to one that is 1.22 times as heavy.... ie instead of 7.9 gr. that would be 7.9 x 1.22 = 9.6 grains.... In other words, a 14.3 gr. pellet in .22 cal would act like a 9.6 gr. pellet in .177 cal in terms of how much air pressure it takes to start it to move and how it will accelerate (initially) down the barrel....
Want to double check these figures to see if they make sense in the real world?.... Take a .22 Springer that launches a 14.3 gr. pellet at 700 fps.... What velocity should be expect in .177 cal?.... Roughly 700 x 1.22 = 854 fps with a 7.9 gr.... Sure sounds about right from my experience....
Incidently.... If we look at the FPE developed by the Springer in the example above.... we get 15.6 FPE in .22 cal and just 12.8 FPE in .177 cal.... ie the .22 cal has 1.22 times the energy.... How about momentum?.... In .22 cal we get 0.0446 compared with 0.0300 in .177 cal.... with the .22 cal coming in at 1.488 times the momentum.... Note that all these numbers work right back to their relationship to the difference in the bore.... and yet also agree with most Springers in the real world....
Bob |
this has been a very good thread. i'd like to add...
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| Posted: Thu Jan 21, 2010 8:57 am |
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| Slavia |
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| I read this so many times my bifocals melted. I think I agree with the steps along the path, but I'm not sure where the path leads. A concluding statement, please? |
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| Posted: Thu Jan 21, 2010 11:37 am |
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| rsterne |
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What is relevant to this thread is.... a 14.3 gr. pellet in .22 cal would load a Springer in much the same way as a 9.6 gr. pellet in .177.... 
Bob |
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_________________
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal: Too many to count! |
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| Posted: Thu Jan 21, 2010 5:27 pm |
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| Slavia |
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| Thanks! All is clear now. |
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| Posted: Tue Feb 02, 2010 10:36 am |
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| Lipoly |
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I apologize for raising this from the dead(although recently deceased) , but the topic was linked in another thread which prompted me to try and wrap my feeble brain around the concept again.
| rsterne wrote: |
To compare a .22 pellet to a .177 pellet, we would have to compare it to one that is 1.22 times as heavy....
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I understand how the relationship between the diameter of the two calibers is 1.22, and how this relates to their weights, but how did you come to the conclusion that .177 pellets need to weight 1.22 times as much to load similarly to a .22? I apologize if you covered it, but every other assertion is pretty clear to me except this one.
| rsterne wrote: |
In other words, a 14.3 gr. pellet in .22 cal would act like a 9.6 gr. pellet in .177 cal in terms of how much air pressure it takes to start it to move and how it will accelerate (initially) down the barrel....
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It sounds reasonable that they would begin moving at the same time, but even initially I'd think the 9.6gr pellet would be accelerating faster than the 14.3gr one (since I'm under the assumption that the 9.6gr one would achieve higher max velocity).
| rsterne wrote: |
Well, the base area of the pellet goes up by the square of the diameter.... or 1.22 x 1.22 = 1.488 times.... Since the force the air pressure can exert on the pellet equals the pressure times the area.... the air pressure exerts ~49% more force on a .22 pellet than on a .177 pellet....
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The pellet area in contact with the barrel obviously goes up as well...I wonder how much this plays into the equation
Doesn't all this suggest that given (lets say) a 14.3gr pellet in both .22 and .177 calibers the .22 will achieve a higher peak velocity?
Since the empirical evidence suggests you are correct, I'm not by any means denying it, just trying to understand it. |
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_________________
Philip
RWS 350 .22 w/Leapers 4-16x50
Crossman 1377 |
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| Posted: Wed Jun 15, 2011 5:43 am |
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| Jr. Squirreler |
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| I shoot 10Grain Crosman Heavy Domed and my Spring has neverrr cocked itself back |
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