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Thread: Pellet doping

  1. #21
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    Water and oil don't mix without an emulsifier - and would eventually separate.

    Plastics outgass - this is because as the polymer stabilizes and crystalizes, the chains become tighter and release molecules. This is also why some plastics "sweat" and smell. Newly cast and extruded plastics do this to stabilize, old plastics tend to crack and break down because over time, those chains break down. Outgassing is not an exothermic process.

    A smoking point is a temperature where a combustible liquid begins to break down. This term is usually reserved for cooking oils...

    A flash point is a temperature at which a flammable liquid vaporizes and can ignite. i.e. FAE. If you don't know what that is, look it up. It is scary.

    Ignition point - the minimum temperature where a substance will burn and remain burning without application of more energy (heat). this is the point where if it burns, it will continue to burn on its own.

    Dieseling - in an airgun, it means that there is fuel somewhere in the compression chamber. Pressure Volume and Temperature are directly related in this case. As space decreases in the chamber, pressure increases and temperature increases (Your air volume is still the same, just compressed). When the temperature within the volume of space reaches the flash point of the fuel (oil, whatever), the fuel ignites, further increasing pressure and temperature. PV/T.

    Assume you take 6CI of air at room temperature (21C) and normal atmosphere (14psi) and you want to get it to 1000psi. You get:

    P1/T1=P2/T2 (The volume of air is constant)
    14PSI/21Deg=1000PSI/T2
    T2=1500 Degrees. Burn baby burn.

    This is why you don't use anything but synthetic and silicone grease when dealing with HPA. Any hydrocarbon based oil will flash and burn under pressure and increase the pressure very rapidly.

    I suspect that the smoke you are seeing is caused by dieseling. IMHO The brown smoke you see is due to impurities and additives to the oil. Steam has no smell.

    You can create a seal (like a gasket) around the pellet's skirt to improve the containment of air by using a little silicone grease. This won't hurt the rifle, but you should always clean up. Once you fire this, you should not see any smoke in the barrel (silicone grease doesn't burn at these temperatures or pressures). I would think that this would improve your velocities (not much... but a bit...)

    Also, you may need to clear the chamber by firing a dozen rounds or so between experiments since the fuel may not all burn away at once. If you find your rifle still has smoke in the barrel after a few shots - and you have not lubed your pellets... chances are, you're dieseling.

    Dieseling is bad. It causes damage to the piston seal as well as the spring and compression cylinder. For a new airgun, it helps break it in, but doing it constantly will gut your rifle.

    Try out the silicon grease... I want to see what your results would be.
    Cheers!

  2. #22
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    MAECOLIS
    Red youre responce, excellent we may figure out whats relly hapening with this experiment.
    I am using cooking oils/salad oils for this project,nothing with any petrolium base.Youre standard bottle of MAZOLLA CORN OIL is the base oil (used as a standard for comparison).
    Last gun used for this test was a new hw80k stock.h&n baracuda 22 cal. pellet; no doping.Speed 588 av. doped speed 700 av.Second pellet Daystate range master 15 gr.Pellet only speed 732 av. doped 925 av.This gun is now fitted with a VORTEK KIT.I
    have only fired it with std. pellets.
    Will try the grease sugestion as this may answer another question i have with this particular gun.
    HAVE A GOOD DAY AND THANKS

  3. #23
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    Forgot to mention :80 k never fired with doped pellet and vortec kit.

  4. #24
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    Cooking oil has a higher flash point than petroleum based oils... But it will still ignite and it will still burn. Petroleum oils are organic matter that have undergone slow processes over millions of years. You can, for example, use old cooking oil to run your diesel engine car. Just strain it first.

    All new springers will diesel the first few dozen shots... Usually less. To be sure of your results, make sure your rifle is past this stage before you experiment.

  5. #25
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    The rifle is long past this point.I know what youre talling me.

  6. #26
    Senior Member sholo's Avatar
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    Quote Originally Posted by maurice View Post
    MAECOLIS

    Last gun used for this test was a new hw80k stock.h&n baracuda 22 cal. pellet; no doping.Speed 588 av. doped speed 700 av.Second pellet Daystate range master 15 gr.Pellet only speed 732 av. doped 925 av.
    That's a significant jump in fps. I thought maybe 40-50 fps max, but your #'s are impressive! Might have to look into this further.Great thread, BTW
    Todd

    Don't sweat the petty things, and don't pet the sweatty things!

  7. #27
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    Assume you take 6CI of air at room temperature (21C) and normal atmosphere (14psi) and you want to get it to 1000psi. You get:

    P1/T1=P2/T2 (The volume of air is constant)
    14PSI/21Deg=1000PSI/T2
    T2=1500 Degrees.
    This ideal gas law treatment isn't quite correct as the volume changes. The amount of air is the same but the volume it occupies is smaller. Work has also been done on the air.

    If you look at it as essentially an isentropic process (reversible and adiabatic(no heat transfer in or out)) which means no change in entropy, and use the equation for entropy of a gas:

    entropy eqn.png

    Since delta S equals zero (no change in entropy) the equation can be rearranged to:

    T = T0e(Rln(P/P0)/Cp)

    Where
    T=final temp (degrees Kelvin)
    T0=initial temp (degrees Kelvin) = 21+273=294
    R= the gas constant = 8.314 kJ/kmol degC
    P=initial pressure (pascals) = 101,325
    P0=final pressure (pascals) = 6,894,747
    Cp=specific heat = 29.248 kJ/kmol degC

    A quick plug and crank and:

    T= 975.7K or 702.7 degrees C

    Still pretty hot.

    It is also important to use absolute temperatures particularly when taking any ratios and use consistently SI or Imperial units. Hope this helps.

  8. #28
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    I will dig out the records i kept when this project started.An interesting point is, the gun used for 90% of the test is a benje classic 22 non PAL.A quest 500 is the same gun PAL rated. I purchased the appropriate piston (4 inch stroke classic is only 2inch) the only other mod is the transfer port was drilled out to .125/1/8" of an inch.
    I will post this info later this evening or tomorrow morning.Anyone paying any interest to this post will notice something peculiar with the numbers and the guns.
    PS my spelling will improve (eventually) i"ts a ***** typing with 2 fingers and bifocles and the first time i ever signed onto a web site.HAVE FUN YOU GUYS.

  9. #29
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    Heyya MSE01,

    You are absolutely correct about your formulas. I'm just keeping it as simple and as quick as I can without a physics lesson... :) But you are right - SI and SAE don't mix... In the case of the ideal gas law, since it's a simple ratio, I felt I could cheat a little.

    Note that 700 degrees C is about the temperature you heat treat steel at... and corn oil flashes at about 327 degrees C... :)

    Maurice,

    Don't worry about the spelling - it's the info that counts. :)

    Cheers!

  10. #30
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    Some more info on pellet doping.

    Test rifle:BENJAMIN CLASSIC 22.New piston installed know 4 inch stroke (fac rated) Same as QUEST 500.Transfer port enlarged to .125".Gun temperature at breach, action closed.
    Measured with COLE-PALMER 18" long probe thermometer 68 F.Test performed indoors.Test chrony ALPHA MODEL recallibrated at repair center for max. accuracy betwean
    350 fps thrue to 1000 fps.Rifle was dismantled and cleaned and re lubed.Approx pellets prior to doping tests 1000.

    All tests:10 shot strings min.

    Test no.1 CROW MAGNUM pellet wheight 18.2 gr.Scale wheight.
    Pellet only:630 fps DOPED 800 FPS and this is only with a 50/50 drop of corn oil (refined) non refined will yield faster results.

    Test no.2 BARACUDA pellet wheight 21.1 Scale wheight.
    Pellet only:556 fps DOPED 750 FPS this is with a droplet of corn oil.Wet only (volume of oil on back of pellet) will yield 600FPS.

    Other pellets have been tested with varius amounts of oil; problem being speeds and pellet wheight are of no usefull use to an airguner.To fast insuficient pellet wheight to
    much air drag at speed nothing left usable at 50 yards, (50 YARDS IS MY BENCHMARK FOR ALL TESTS AND ANY EVALUATION OF ANY AIRGUN).

    Doping application procedure.
    A SYRINGE:these may be purchased at LEE VALLEY TOOLS they are used for applying glue in verry small cracks in wood (furniture repair).The tip of these units are not s
    slant cut, square ends.They come with 3 tip sizes; i only use the pink one, smallest one.Due to pellet skirt size and desighn EG. deep skirt for BARACUDA shallow skirt f
    for CROSMAN pellets, they act differently with varying amounts of oil.YOU CANNOT OVER DU IT the process will not work.To much oil you may gain 50 FPS.
    Remember the information above only applys to the formentioned airgun.

    This article is not about power tripping, you want power; buy a talon tuned 25 cal maxed out.

    ANYWAYS HAVE A GOOD DAY HOPE YOU ENJOY THE INFO.

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