What am I missing?

Forums General Discussion What am I missing?

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    Yarddog
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    But…why?

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    ptthere
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    wyshadow

    You can get much higher pressures with a chemical explosion then with compressed breathable air. 

    This.

    Gunpowder releases energy when ignited by being fueled by oxygen via the chemical breakdown of potassium nitrate after ignition. Being trapped in a barrel behind a bullet causes compression, which allows the potassium nitrate and sulfur and other chemicals to deflagrate even faster with the hot gases trying to expand, causing more pressure, causing the "burn" to accelerate even faster, causing more expansion, causing even more hot gases under pressure, etc.

    Compressed air can only be compressed so much until it is impractical and/or useless to achieve higher pressures. If you could compress air high enough to achieve the pressures needed to achieve the ballistics you are looking for, you would encounter three major problems: 1., How to safely contain the pressure in a vessel and the entire firing chain. 2., How to safely compress the air/gas without creating excessive heat. 3., How to discharge the air without rapid cooling and freezing everything in the transfer port and barrel from the rapid and violent expansion. Some of the gases, specifically the Nitrogen, Oxygen, and CO2, could very well freeze as a temporarily solid upon discharge when going from extremely high pressure to atmosphere.

    Without going into a more in-depth physics and chemistry lesson, I can't see it ever being feasible to replace gunpowder with just air. If someone made a barrel that was bored to truly fit a .17 HMR round for airgun purposes, I am sure it wouldn't be too hard to push that 17- or 20-grain projectile upwards of 1000 fps, but it takes an exponentially larger amount of energy to even think about 2800 fps, the type of energy that regular air cannot produce without a chemical reaction. As someone else stated, it really is like comparing apples to bowling balls.

    PT

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    Quad82
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     I have not heard of this before, but what if? You had multiple air tubes with valves with transfer ports on multiple sides of a barrel all firing at the same time. Something like having multiple cylinders on a black powder handgun firing at the same time. Only funneling the pressure down a barrel instead of into the frame. Ya, it’s happened to me. Some sealers work better than others! I realize this would be impractical. But would it be possible?

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    ptthere
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    Quad82

     I have not heard of this before, but what if? You had multiple air tubes with valves with transfer ports on multiple sides of a barrel all firing at the same time. Something like having multiple cylinders on a black powder handgun firing at the same time. Only funneling the pressure down a barrel instead of into the frame. Ya, it’s happened to me. Some sealers work better than others! I realize this would be impractical. But would it be possible?

    Even if all were at 3000 PSI, fired at the same time, the total pressure would still be 3000 PSI.

    PT

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    boscoebrea
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    +I remember when I was curious as to why not,I even studied it and I found out others had thoughts of the same thing.

    I keep on reading and asking and the end result was that it was not practical,cost too much .was not safe and there were already things called firearms,yet I was shown air cannons and things were possible,butt again were not practical ..I have dealt with high pressure air for many years,it is dangerous and can cut you into two,then there was the time a a life boat bottle got away and went through the wall and thus we lost our contract to repair life boats….air tools work great and we never ran out of air and in all those years I never saw an air compressor where the heck did all that air come from,,,btw it was at a large Navy shipyard. and please excuse my excursion into the past.

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    SteveV
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    Great post, thread, question, and answers – thank you AGN!

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    lenweber2
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    HAVE you ever shot sabots? Many moons ago I did .22 in 30cal and .308 in a big bore. If you were hunting barns you would need a good stauking ability. If one had enough hipressure air and a long enough barrel, like many feet long, in tens of feet one might get a long enough acceleration time high speed might be the reward. Let us know what the cost to build such a barrel and bore cutting would cost. The bullets would need to be copper lead or copper as near 2000 fps lead smear would need to be felt with.

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    Broken_WV_Guy
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    I've read all the comments and appreciate the feedback. I don't even own an good air rifle yet. I'm recently disabled and have been looking for something I can physically do while spending time with my 9 year old daughter. She loves plinking with me but quickly gets bored waiting for me to pump the gun and reload for her. I live in WV and grew up hunting but can't shoot anything that has recoil if I want to be able to walk the next day. I've been overwhelmed by all the PCP options out there and as soon as I think I know what I want to get as a starter gun, I see another model to compare. It might take me a long time to acquire all the components needed but this is definitely a hobby I plan to get into. I competed in three position pellet in High School and would love to send my daughter to WVU on a shooting scholarship one day.

    After doing some math I've come to the conclusion that we are actually a lot closer to achieving my main goal than we might think. Especially on "overpowered" air guns designed to shoot slugs. My degree is in EE but i've never worked as an Engineer so my math is beyond rusty.

    I'm also having a hard time finding the minimum fps a .17hmr remains stable. If someone knows that value, please fill me in. I need it to calculate the end target fps so we can work backwards to get the minimum barrel fps. Mass will obviously affect it as well but at least it's a starting point.
     

    When I was first thinking about this, I was considering why won't don't shoot a standard .17HMR round with air. After looking at the data, that round simply has too much mass, not enough surface area/caliber and the target 2800 fps just wouldn't be possible without complicating the process, as several of you have said.

    However, a 15.5g .17hmr round fired from a gun will only be traveling at 1070 fps at 200 yards and still fully stable. So if we forget about 2800 fps and forget about matching the ballistic properties of a firearm. Can we simply create a gyroscopic and dynamic stabilized round from PCP?

    What if lightweight alloy was used to minimize the mass of the round, but used the shape of a gun projectile and the appropriate twist rate was used on the barrel?

    What FPS could we get?
    Would it be stable and accurate?
    How much range would it have?
    Would it out perform a .177 pellet?
    Would we be able to scale the design to .22, .25 etc?
    Would a heavy slug out perform it?
    Would a different shape be more effective?(fins, sabot, etc)

    We all know pellets use drag to create stability. While they work great, I consider the diablo or hourglass shape to be inferior to a gyroscopic and dynamic stabilized round. For those of you asking "Why", it was because today there are air rifles powerful enough to blast pellets far beyond the stability of the diablo shape. FPS is limited by the pellet shape and I'm confident there will be new projectiles created to take advantage of all that power.

    For me, the .17hrm was the obvious choice to start exploring this further and again I thank you all for the feedback. I wish I had the tools to further develop the concept but I'm positive there are lots of people more capable than myself who will figure it all out. It's probably a lot closer than anyone knows because if someone were to develop such a round, they wouldn't want to advertise it until it went to market or patents were approved.

    I don't think it's if, but when. Higher FPS from air is coming.

     

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    bucketboy
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    The problem as I see it is,,, regardless of how big the transfer port is or how many ports there are the air still has to travel up a 4.5mm bore of the barrel, the barrel needs to be long enough get the projectile up to speed but the longer the barrel the harder it is for the air to squeeze through.

    while it is easier to get a lighter projectile up to speed it will loose speed much more quickly on route to the target.

     

    best of luck

     

    Bb

    • This reply was modified 3 months ago by bucketboy.
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    Broken_WV_Guy
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    This was what I was missing. Lack of stability in the transonic region.

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    ptthere
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    Broken_WV_Guy

    This was what I was missing. Lack of stability in the transonic region.
     

     

    Yes sir, this is a PITA for anything that crosses the sound barrier. Approaching mach 1 puts a lot of dynamic stress on an object, but that stress drops off just as quick after exceeding mach 1, and vice-versa.

    PT

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    Saltlake58
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    I'm no engineer, but to be honest, the physics of shooting an airgun pellet at 2800fps just don't seem to be there.  Even if you opened the transfer port to the size of the projectile (and barrel), it's only 3000 PSI maybe 5000 PSI if you really push it.  I haven't found what I'd call solid information about the chamber pressure of a 17 HMR, but what I have found is 26,000 PSI.  Just look at the thickness of the chamber around a 17 HMR vs a .177 air rifle.  26,000 PSI would blow the sides out.

    If you really want high power, you'd probably need to shift from air to helium.  Watch this one: https://www.youtube.com/watch?v=ajBT2V4_rrk.  Big bore running helium because it compresses better than air.  You could probably convert a standard gun to helium, but that would put you way outside the gun specifications unless you build it yourself.

    basic physics seem to be against matching 17 HMR performance with an airgun.  Just can't get the ooooomph out of the airgun.  

     

     

     

     

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    Peskadot671
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    ☝🏽

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    Willie14228
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    Unfortunately we have to follow the laws of physics ☹️

    Think of a river, how to do turn a calm gentle river into a raging rapids , you go from a 1/2 mile wide down to a 1/4 mile. Dennis quackenbush actually worked on a little project of his own in which he took some very light material and laid it down to bullet size and as a result was able to get it at like 1800 feet per second still consider this if you were to take a golf ball and a ping pong ball which would you rather be hit with a ping pong ball traveling at 1000 feet per second or golf ball traveling at 500 feet per second by the time the ping pong ball reached you due to its weight and surface area producing drag it would have already lost much of its momentum vice versa the golf ball because of its weight even though it is very similar in dimensions of a ping pong ball would still be traveling much closer to its muzzle velocity further due to its weight it's going to hit a lot harder.

    There's another consideration that you have to put in your mind and it's actually one of the reasons why you're getting such a knee-jerk reaction from other members and that is we don't want an air gun with the abilities of a firearm in such a case it's almost definite that the result will be laws passed restricting air guns and requirements of licensing in permitting. 

    Firearms have their place and air rifles has theirs let's keep them in their place so that everyone can enjoy them the way they want to when we began crossing boundaries that you are discussing the line becomes very blurred between an air gun and a firearm.

    Scientifically your ideas are interesting but at our current level of technology and engineering abilities outside of our scope.

    There is a potential possibility in a hybrid air gun using rail gun technology combined with air

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    fuznut
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    Take a look at the gains black powder has made due to the sabot. Am dumb enough to think air could too. No need to reinvent the air gun to make a major advancement. But yeah big bore stands to benefit the most.

    Doing nothing in the hopes of avoiding tighter regulations,  really? Happy new year all !!! Lets hope its a good one.

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    MikeinWV
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    Just a wacky thought….what about flammable compressed gas with combustion behind the pellet/projectile?  Electronic firing via some sort of igniter.  I suspect that even if these sort of pipe dreams were possible there would be limiting factors of diminished returns ie..pressure deforming the tail of the projectile or high pressure and velocity disintegration of projectile.

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    JimNM
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    MikeinWV

    Just a wacky thought….what about flammable compressed gas with combustion behind the pellet/projectile?  Electronic firing via some sort of igniter.  I suspect that even if these sort of pipe dreams were possible there would be limiting factors of diminished returns ie..pressure deforming the tail of the projectile or high pressure and velocity disintegration of projectile.

    By definition, adding fire (combustion, conflagration, explosion) creates a firearm.  No bueno.  Even causing your spring piston airgun to diesel on purpose creates a FIREarm due to the combustion of a fuel to propel the pellet.  That is a topic that is not welcome on AIRGUN forums. 

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    ptthere
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    MikeinWV

    Just a wacky thought….what about flammable compressed gas with combustion behind the pellet/projectile?  Electronic firing via some sort of igniter.  I suspect that even if these sort of pipe dreams were possible there would be limiting factors of diminished returns ie..pressure deforming the tail of the projectile or high pressure and velocity disintegration of projectile.

    That's a murky "grey" area in terms of legality. Airguns can be "dieseled" when the user accidentally uses a flammable lubricant or solvent to clean the barrel, and forgets to remove much of it before firing it. This causes it to detonate under pressure on the first few shots and can give the pellet several hundred FPS more from the barrel, although accuracy usually suffers quite a bit as the pellet moves supersonic and slows down through the trans-sonic range.

    If a manufacturer offered what you are describing as an INTENDED option, the ATF would call it a firearm and shut it down. They have done so before several decades ago (I forget which model of airgun it was).

    If it was simply dieseling by the user and still used for "recreational" purposes, I don't see the ATF considering it as a firearm if you were shooting at paper or some other static targets. For instance, "spud guns" fired with propellant and generally considered legal on a federal level, but I am sure there are some local municipalities in this country that ban them like anything else. But if you had INTENT to use the air rifle in that manner and it caused harm to someone else, you may find yourself in quite the legal predicament, even if you are the first guy to ever fall under that axe. There's also a multitude of other practical reasons why many air rifles would eventually suffer from shooting them in this regard.

    I wouldn't do it on purpose and I would not recommend it here or anywhere else. Different forums may be more suited to discuss a concept like that with other firearms.

    PT

    • This reply was modified 3 months ago by ptthere.
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    Broken_WV_Guy
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    Appreciate the ideas but I was more interested in gyroscopic stability than matching powder burning velocities with air. The transonic instability just means that any progress in this area will have to jump to over 1200 fps at the target. Once we can get a projectile moving that fast at range, we would have the option of using similar shaped bullets.

    I know any real progress would cause complication, but my idea was to create a metered and regulated chamber that could be compressed using hydraulic multiplication to greatly raise the PSI of each shot. This should be enough power, but we will let the manufactures figure that out. Whatever comes next, it's going to be moving faster than what we can do today.

     

     

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    ptthere
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    Broken_WV_Guy

    Appreciate the ideas but I was more interested in gyroscopic stability than matching powder burning velocities with air. The transonic instability just means that any progress in this area will have to jump to over 1200 fps at the target. Once we can get a projectile moving that fast at range, we would have the option of using similar shaped bullets.

    I know any real progress would cause complication, but my idea was to create a metered and regulated chamber that could be compressed using hydraulic multiplication to greatly raise the PSI of each shot. This should be enough power, but we will let the manufactures figure that out. Whatever comes next, it's going to be moving faster than what we can do today.

     

     

    That's one of the more realistic responses I have seen. Using hydraulics and boosters, you CAN compress air well over 20,000 psi or more, however you would also need some seriously badass seals to hold the air pressure back beyond whatever you were using as a piston within a cylinder/tank. Similar consideration would have to be made for regulation and dispensing air for shots.

    The other problem as I mentioned before would also be thermal issues. During compression, considerable heat would be generated with the air. During firing, agressive cooling would be taking place in very short intervals, and a mild study in physics and thermal dynamics might be of use to consider ways to negotiate and overcome these issues.

    But, the hydraulic idea is still interesting. You probably would not achieve firearm levels of performance, but it could certainly be done above what is usually handled with 3000/4500-lb tanks.

    PT

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