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Thread: Shots per charge

  1. #1
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    Default Shots per charge

    Hi, am i correct in saying that a .22 rifle gets more shots per charge than a .177? Say for instance you take 2 identical rifles except one is .22 and the other .177, both at 12ftlbs, the .22 rifle will get more shots per charge than the .177.

    Will this be the same with heavy and lighter pellets? Say for instance you take 2 identical rifles both in .177 and both at 12ftlbs. With the one rifle you shoot 8.4gr pellets and the other 10.5gr pellets, will the rifle shooting the heavier pellets get more shots per charge?

    The reason for asking is i was looking at an ad for a rifle, and they advertise the rifle at 1000ft/sec with 25 usable shots per charge. I suppose or assume that the statistics was given for pellets that is not too heavy. So if you use 10.5gr pellets in the rifle, will the shot count go up to maybe 30? Or am i missing something and the shot count will be the same?

    Any input will be appreciated, thanks.
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  2. #2
    Sharp Shooter
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    good question. would love to see the answers on this one..
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  3. #3
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    You will get more shots per fill in a .22 than a .177 all else being equal.

    Not sure about the heavier pellets though. I would assume it would use more air to get a heavier pellet to the same velocity a lighter one.
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  4. #4
    Sharp Shooter
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    You are right Dave.. but if you were to shoot a heavier pellet at the same fpe as a lighter (ie: lower velocity) will it use less or more air?
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  5. #5
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    "You are right Dave.. but if you were to shoot a heavier pellet at the same fpe as a lighter (ie: lower velocity) will it use less or more air?"

    I have no idea! impgrin
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  6. #6
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    In unregulated PCP rifles the amount of air released is determined by the length of time the valve is held open by the firing mechanism. Since this would be the same (at a given cylinder pressure) irrespective of pellet, the heavier pellet would simply move slower and the shot count would be the same.
    Try sucking liquid through a thin or thick straw - Much easier with a thick straw. The .22 gives more shots because you need less air to impart the same velocity on the larger diameter pellet. Pressure is a function of Area. That is why you get more shots with a .22, not because it is heavier.
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  7. #7
    Sharp Shooter
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    tomcat.. I believe, applying some logic to the system, that the reason the larger pellet uses less air is because it takes longer to get going. hence less air can get out the valve before it closes again. This makes me think that the heavier grain pellet will use less air as well. I know the .22 pellet are much more efficient at using air because of the skirt diameter.. but back to the question.. I think the heavier pellet will use less air but will also be slower ofcourse.
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  8. #8
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    JTK, your logic is interesting, but flawed because it is based on incorrect assumptions. The reason the .22 uses less air, is because the air is used more eficiently in the larger bored barrel. The fact that the pellet gets going more slowly does not affect the amount of air that is released by the striker. The air comes out under extremely high pressure which gets the pellet moving virtually immediately.
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  9. #9
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    Hi Tomcat, your explenation made perfectly sense to me about the length of time the valve stays open so the air consumpsion will be the same, until i read JTK's answer, and he's got a point.

    If i understand JTK correctly, the bigger or heavier pellet will give more resistance or back pressure than the lighter or smaller pellet.

    The lighter pellet will move faster, so for the time the valve is open the pellet will have moved for instance 20cm down the barrel before the valve closes again and that will equal an X amount of air that escaped from the valve. In other words the volume of air from the valve to the pellet is 20cm of "barrel space"

    Now the heavier pellet gives more resistance and therefore moves slower so for the same time the valve is open the pellet would have moved for arguments sake only 15cm down the barrel which will be Y amount of air from the valve to the pellet.

    X is more than Y or am i still missing something here?
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  10. #10
    Sharp Shooter
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    Rowan

    The mere fact that you are trying to compare two identical rifles, with one being .22 and the other .177 makes it very tricky, because they are not identical anymore.....!!!!!
    Regarding your second theoretical assumption about using light or heavier pellets, it again depends whether the rifles are tuned to optimal efficiency to start with.....
    In principle what TomCat and TDK replied sound about right, but it again depends whether the rifles in question were tuned to optimal settings, both in efficient air useage, as well as power output per pellet weight....
    Efficiency factor means different things to different people, I measure it by total bars used in firing the shots times reservoir volume, divided by power level at which the shots were fired and divided again by number of shots.....
    Typically a .177 cal would give you 12.2 and a .22 cal would give you 14.2.....
    If that makes the .22 more efficient, then so be it......!!!!!

    malan
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  11. #11
    Sharp Shooter
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    Aggreed.. But someone with a chrony please give it a bash to satisfy the curiosity Shoot 7grains from full presure to the empty and see where fps start to vary to much. then shoot 10.4 grains and see which one gives you more shots..
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  12. #12
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    Hi Malan,

    I just used the .177 and .22 to demonstrate that a .22 at 12ftlbs gets more shots than a .177 at 12ftlbs, i was not trying to compare them. What i am trying to find out is why the .22 is more effecient, is it because of the size of the pellet or the weight of the pellet? Or is it more complicated than that?

    JTK, i will love to do the test but i cannot seem to find light pellets in .20, all the places i have phoned or mailed do not have any stock of the H&N FTT(11.4gr) I only have Crosman Accupels at 14.3gr.
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  13. #13
    Sharp Shooter
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    I will give it a bash when I get my hands on a chrony again.. only problem is the fact that it is an xtra many pellets waisted with the long airtube!
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  14. #14
    Sharp Shooter

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    Ok this is what you will find doing the chrony testing. You will almost certainly get the same number of shots using the same rifle and different pellets, because of tomcats statement that the valve stays open for a certain amount of time. What you also should find is that your heavy pellet is running more efficiently thus giving more power. This is because the heavy pellet is travelling slower and the air can transfer more energy to the heavy pellet.

    So given that, to get the same power output from a heavy pellet the rifle will have to be tuned down a bit. Because it is tuned down it will give more shots for the same power output from heavy pellets.

    Also the bore diameter does affect efficiency and the bigger the better. What is more important at 12fpe however is the "barrel time" of the pellet, the heavy .22 pellet will have more barrel time thus more energy can be transferred from the air to the pellet. Considering this a heavy .177 pellet and very light .22 pellet (both having the same weight) would produce efficiencies very close to each other considering pcp's shooting at 12fpe (with the .22 with a slight advantage because of bore size)

    This was however just for pcp's where the air acts slowly on the pellet. On springers and rams the bore size has a much bigger influence because of the short burst of air.

    If you would like to compare these with powder burning rifles,
    pcp's are like modern rifles firing smokeless powder (a propellant) and springers are like muzzle loaders firing black powder (an explosive)
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  15. #15
    Sharp Shooter
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    Thanks Arnold.. You dont think the heavier pellet will cause less air to exit the valve at the same open time? because of more back presure? Or is this not significant enough to measure?
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