Home-made Air gun / rifle
Rizla99
"213546546" <546...@6584.1548> wrote in message
news:Xns93CE1F468C...@193.38.113.46...
> Hi!
> Does anyone have any information or *plans* as to making a spring piston
> based air rifle?? [based on human power??] Preferably auto-loading?
>
> I'm just thinking of designing a cheapo, for fun gun with a cheapo
> spring, home made magazine of cheapo pellets like say, old batteries
> [mebbe too heavy] etc.
>
> Just curious as to if there are any plans out there before trying to
> solve certain problems myself like how to cock the piston without
> letting air escape from a handle I use to cock it or making it quick
> reload, mebbe even auto reload [plonk a spring in the mag to auto reload
> after cocking it?] etc.
>
> Any info would be greatly appreciated.
>
>
-------------------------
How a regulator works
http://www.warpig.com/paintball/technical/regulators/howtheywork/index.shtml
Not How To Build an Air Cannon
http://www.corin.com/bill/paintball/aircannon/ Just scale it down maybe !
General info here http://www.airguns.net/general.html
You might find something here
http://www.frugalsquirrels.com/survival-lib/firearms-pyro.html
Or one of the other links on this page
http://www.frugalsquirrels.com/survival-lib.html
Those links should help to get you started, or even get you on national TV
if you try to build the A Bomb listed on one of those links :-)
Good luck & have fun, but remember,....... Safety First!
Trevor Jones
>
> Hi!
> Does anyone have any information or *plans* as to making a spring piston
> based air rifle?? [based on human power??] Preferably auto-loading?
>
> I'm just thinking of designing a cheapo, for fun gun with a cheapo
> spring, home made magazine of cheapo pellets like say, old batteries
> [mebbe too heavy] etc.
>
> Just curious as to if there are any plans out there before trying to
> solve certain problems myself like how to cock the piston without
> letting air escape from a handle I use to cock it or making it quick
> reload, mebbe even auto reload [plonk a spring in the mag to auto reload
> after cocking it?] etc.
>
> Any info would be greatly appreciated.
Probably a good time for you to brush up on your basic physics. Pay
particular attention to the principles of kinetic and potential energy.
Remember that you will have to cock the spring to store enough
potential energy in order to use it to produce kinetic energy. You will
NOT get more energy out than you put in. (losses due to friction, gas
flow dynamics,etc).
Consider that the top end spring piston guns fron the best makers in
the world are producing around 25 or so Ft/Lbs of energy, and are
considered hard to cock for an average adult. To fling anything of any
weight at useable velocities, you will have to design a very robust
mechanism.
Far better possibilities are available in dealing with CO2 or
compressed air power. In those, efficiency actually improves somewhat
when the bore size is increased and the weight of the projectile goes
up. Note that being efficient is not the same as being useful, merely
that the efficient guns produce more energy output than the not
efficient ones, for a given energy input.
An area to look at that is well whithin the realms of the realistic is
the designs like old BB guns. A person could build some pretty decent
stuff to shoot airsoft (6mm) or steel BB's (.177 cal) in the backyard
without having to deal with a mechanism that contains enough potential
energy so as to be a risk to ones own life if it comes apart while being
held next to ones face.
As far as I know, there are no plans for spring piston guns available.
A chap in England has a book available with drawings of a PCP air rifle,
but I do not know much other than that about it. There are a pile of
guys building PCP and CO2 guns, but few if any are selling plans.
Cheers
Trevor Jones
Isaac Kuo
news:Xns93CE1F468C...@193.38.113.46...
> Does anyone have any information or *plans* as to making a spring piston
> based air rifle?? [based on human power??] Preferably auto-loading?
> I'm just thinking of designing a cheapo, for fun gun with a cheapo
> spring, home made magazine of cheapo pellets like say, old batteries
> [mebbe too heavy] etc.
A spring piston design, while seemingly simple, is not so
easy to make from scratch. It's easier to make a compressed
air gun, pumped up via a bicycle pump.
For a compressed air gun, all you really need is a couple
PVC pipes, a ball valve, a tire valve, and some fittings
to connect them together. There are also ways to adapt
sprinkler valves or making your own valves to improve
power, efficiency, and accuracy (the force and movement
required to manually open a ball valve quickly makes accuracy
more or less impossible).
If you think using a premade bicycle pump is "cheating",
then it's still easier to first make your own air pump and
use it to charge a compressed air gun than it is to make
a spring piston. A homemade air pump piston can afford to
be slow and rather inefficient (due to friction). A spring
piston can't.
However, the tough part of a homemade air pump is the one
way valve required at the end (the piston sealing material
does double duty as the other one way valve). You can
avoid any need for a one way valve by designing your airgun
as a single stroke gas piston design. In this case, the
piston is stroked only once, compressing a single tubeful
of air. This piston is mechanically held closed somehow.
Then the ball valve (or some other more sophisticated valve)
releases this air into the barrel to fire.
I'd still recommend making the bicycle pump charged air gun
first, even if your ultimate goal is to make this single
stroke design. It will give you a feel for how big the
various components need to be and how much power you can
get out of it. For example, if you find that you like the
amount of power available from 3 pumps of the bicycle pump,
calculate the volume of air you pumped based on the cross
sectional area of the pump and the total distance you pressed
the pump handle downward. You'll need your main cylinder
to compress the same total volume. Note that you can
reduce the length of your tube by increasing the diameter
compared to the bicycle pump, but this will also increace
the amount of force required!
Isaac Kuo
213546546
an interplexing subspace beacon on subspace frequency
news:acc26c07.0308...@posting.google.com on stardate 05 Aug 2003
> "213546546" <546...@6584.1548> wrote in message
> news:Xns93CE1F468C...@193.38.113.46...
>
> A spring piston design, while seemingly simple, is not so
> easy to make from scratch. It's easier to make a compressed
> air gun, pumped up via a bicycle pump.
Thanks, I considered this once, but threw the idea out due to bulkiness and
also the lack of safety [imho!] ; I did not want to risk my life on a
simple safety valve which could malfunction and explode!
But, since it may tell me how much volume of air needs to be compressed to
propel a projectile, I shall consider it.
Thanks for the replies folks!
#MK
> 213546546 wrote:
>>
>
> Probably a good time for you to brush up on your basic physics. Pay
> particular attention to the principles of kinetic and potential energy.
>
> Remember that you will have to cock the spring to store enough
> potential energy in order to use it to produce kinetic energy. You will
> NOT get more energy out than you put in. (losses due to friction, gas
> flow dynamics,etc).
Yes, I am aware of this, being a longbow shooter too! I was wondering,
would an air rifle need more potential energy from my arm than a longbow to
achieve similar velocities? I.e. is it more or less efficient than a
longbow? [I don't really need huge power that is gained via a compressed
air resevoir thingy as I don't intend to kill things. This project is just
a bit of fun to see how functional I can make an air rifle at home! hehe]
Since a longbow works on a similar prinicple of a spring, in the form of a
bow, being compressed [and tensioned] and then return back to its original
shape to store and release the energy from my arm, I once read somewhere
that rather than having a spring *directly* push a projectile, it is more
efficient if the spring "pushes" or compresses the *air* behind it....
Is this true?
Joseph Oberlander
> Consider that the top end spring piston guns fron the best makers in
> the world are producing around 25 or so Ft/Lbs of energy, and are
> considered hard to cock for an average adult. To fling anything of any
> weight at useable velocities, you will have to design a very robust
> mechanism.
He could use a ratchet type system like they used on large crossbows
and balistas. - it compressed air is far better. They make cannons
that will launch a pumpkin a quarter of a mile now. The same guns
using a formed projectile and a rifled barrel? Several miles.
So building something smaller is possible, though not necessarily
easy.
gfddfgfgfg
> So building something smaller is possible, though not necessarily
> easy.
>
Is a longbow / crossbow more efficiently than a similar spring piston-based
airgun? After all one utilises the force to compress air which then
"pushes" the projectile whilst the other DIRECTLY pushes the projectile in
a bow.
So, surely one can be made which requires similar forces to cock and gives
similar velocity>?>>
Isaac Kuo
> mec...@yahoo.com (Isaac Kuo) transmitted the following communciation via
> an interplexing subspace beacon on subspace frequency
> news:acc26c07.0308...@posting.google.com on stardate 05 Aug 2003
> > A spring piston design, while seemingly simple, is not so
> > easy to make from scratch. It's easier to make a compressed
> > air gun, pumped up via a bicycle pump.
> Thanks, I considered this once, but threw the idea out due to bulkiness and
> also the lack of safety [imho!] ; I did not want to risk my life on a
> simple safety valve which could malfunction and explode!
Actually, a compressed air gun pumped via bicycle pump is safer
than a spring gun. With a bicycle pump, you don't need a safety
valve at all--you're simply not going to be able to physically
pump much more than 80psi or so. You'll use schedule 40 PVC
pipe rated at well over six times that much!
However, let's say there's a weak spot and your compressed air gun
is indeed going to fail. When will this happen? It will happen
when the pressure is highest--when the gun is on the ground a foot
or so away from you, pumping away at the bike pump. With the gun
relatively far away from the user, the chances of injury are very
low. From the moment you stop pumping, the pressure only goes down
(and it starts doing so immediately, as the compressed air cools down).
In contrast, a spring piston gun acheives its highest pressure
as the piston is nearly closed, just before the pressure against
the projectile overcomes the friction holding it back. Here's a
URL with an animated example of how this works:
http://www.eatel.net/~amptech/elecdisc/rifledemos.htm
Scroll all the way down to demo 10. Click on the "continue" button
to step through the animations. Notice how the piston is almost
all the way down the chamber before the pellet starts moving.
How much peak pressure is acheived and when is it acheived? Well,
that depends. If the projectile is light and has little friction
holding it back, the peak pressure will be low. If the projectile
is heavier and has a tight fit for a lot of friction holding it
back, the peak pressure can be much higher than with the bike pump
charged gun. If the projectile rams itself stuck, then the peak
pressure can be very high!
I consider a homemade spring gun unsafe because the peak pressure
may vary a great deal from shot to shot, and isn't inherently
limited to any particular safe level. Furthermore, the peak
pressure occurs upon firing, when the gun is held right up against
the firer's face. If a spring gun fails, it will do so when
there is a good chance of causing injury.
Isaac Kuo
Trevor Jones
>
> Trevor Jones <t.o....@sympatico.ca> transmitted the following
> communciation via an interplexing subspace beacon on subspace frequency
> news:3F2FA723...@sympatico.ca on stardate 05 Aug 2003
>
> > 213546546 wrote:
> >>
> >
> > Probably a good time for you to brush up on your basic physics. Pay
> > particular attention to the principles of kinetic and potential energy.
> >
> > Remember that you will have to cock the spring to store enough
> > potential energy in order to use it to produce kinetic energy. You will
> > NOT get more energy out than you put in. (losses due to friction, gas
> > flow dynamics,etc).
>
> Yes, I am aware of this, being a longbow shooter too! I was wondering,
> would an air rifle need more potential energy from my arm than a longbow to
> achieve similar velocities? I.e. is it more or less efficient than a
> longbow? [I don't really need huge power that is gained via a compressed
> air resevoir thingy as I don't intend to kill things. This project is just
> a bit of fun to see how functional I can make an air rifle at home! hehe]
Think hard about coiling up the equivalent of a longbow and putting it
next to your face. Frankly, I know that I can test a pneumatic mechanism
to a safe enough level (via hydraulic pressure) to make myself feel
reasonably safe with it near me. Lognbows are pretty effective at
transfering energy to their projectile as well.
>
> Since a longbow works on a similar prinicple of a spring, in the form of a
> bow, being compressed [and tensioned] and then return back to its original
> shape to store and release the energy from my arm, I once read somewhere
> that rather than having a spring *directly* push a projectile, it is more
> efficient if the spring "pushes" or compresses the *air* behind it....
Read it where? The bow acts in a physically direct manner on the arrow.
A springer deals with drag and friction while compressing the air, then
the gas flow dynamics while moving the projectile from a standing start
and down the barrel (more friction and drag).
> Is this true?
You tell me. Have you done the math?
You stated that you wished to be able to make a spring gun that would
shoot old batteries, possibly from a repeating magazine. Frankly, I
think if it was practical, it would be available already. The closest
thing that has been built was the repeating crossbows of the distant
past. perhaps you should concentrate your efforts in that direction.
Repeating crossbows or stonebolts, that is.
To reasomably extract the energy available from a single or even double
stroke of the human arm, and convert that energy into kinetic energy in
a projectile is easy. To have it perform its work in a useful manner is
another thing entirely.
Energy equal mass times velocity squared. A light mass (pellet) moving
fast can perform more useful work as a projectile (it flies reasonably
flat, retains some energy at impact) than a heavy mass (battery) with
the same amount of energy to move it(slow, arched trajectory).
Have a time. Personally, I have my doubts as to the likleyhood that
anything will come of this all.
In reality, you could build a springer that could fling batteries.
Likely, you would be into the realms of a coil spring from a car
suspension to get useful amounts of energy from it, and it would be
neither practical nor useful. Not to mention unpleasant to carry or
fire.
Cheers
Trevor Jones
Joseph Oberlander
Except that a bolt/arrow is long and huge and has vanes - because it
has to do all the work that the barrel would normally do.
Now, a piston behind a projectile in a tube(forget the air) would
also work. Of course, pistons are hard to get moving very fast.
You eat a lot in friction and mass losses.
Air has no such problems, and it compresses nicely, so storage
of energy is possible.
Isaac Kuo
> #MK wrote:
> > Yes, I am aware of this, being a longbow shooter too! I was wondering,
> > would an air rifle need more potential energy from my arm than a longbow to
> > achieve similar velocities? I.e. is it more or less efficient than a
> > longbow? [I don't really need huge power that is gained via a compressed
> > air resevoir thingy as I don't intend to kill things. This project is just
> > a bit of fun to see how functional I can make an air rifle at home! hehe]
> Think hard about coiling up the equivalent of a longbow and putting it
> next to your face. Frankly, I know that I can test a pneumatic mechanism
> to a safe enough level (via hydraulic pressure) to make myself feel
> reasonably safe with it near me. Lognbows are pretty effective at
> transfering energy to their projectile as well.
Longbows are only effective if the projectile is relatively heavy
and the intended projectile velocity is relatively low. Otherwise,
too much energy is wasted going into accelerating the string and
bow arms.
While I agree that spring guns are not safe enough, I disagree with
the general assessment to all pneumatic mechanisms. PVC pipe
airguns usually use low pressures far below that at which the PVC
pipe and fittings are rated. This airguns make up for the low
pressure with large chambers and long barrels--but still small
enough to comfortably fit in a rifle-like long arm.
> > Since a longbow works on a similar prinicple of a spring, in the form of a
> > bow, being compressed [and tensioned] and then return back to its original
> > shape to store and release the energy from my arm, I once read somewhere
> > that rather than having a spring *directly* push a projectile, it is more
> > efficient if the spring "pushes" or compresses the *air* behind it....
> Read it where? The bow acts in a physically direct manner on the arrow.
> A springer deals with drag and friction while compressing the air, then
> the gas flow dynamics while moving the projectile from a standing start
> and down the barrel (more friction and drag).
I wouldn't know where he read it, but it's true. There's a reason
spring airguns are spring "airguns" and not just spring guns.
It's because a spring directly pushing a projectile would waste
a lot of energy pushing its own mass to a speed comparable to
that of the projectile. This can only be efficient if the projectile
is a lot heavier than the spring--which in turn puts a sever
limit to projectile velocity because spring metal can only store
so much energy for a given mass.
Instead, a spring airgun mechanism uses pneumatic forces to create
reverse mechanical advantage. Having a large piston move slowly
displaces as much air as a tiny piston moving quickly. Thus, a
strong heavy spring can move slowly to accelerate a light projectile
moving quickly. It doesn't waste much energy accelerating itself
compared to the amount of energy dumped into the projectile. Of
course, some energy is also wasted accelerating the air, but air is
extremely lightweight so most of the energy still gets dumped into
the comparatively much heavier projectile.
> > Is this true?
> You tell me. Have you done the math?
> You stated that you wished to be able to make a spring gun that would
> shoot old batteries, possibly from a repeating magazine. Frankly, I
> think if it was practical, it would be available already.
Well, as far as the practicality of a spring gun repeater goes, there
are plenty of so called "single-shot" airsoft guns. (They're called
"single-shot" within the sport, but they're actually repeaters that
feed from a magazine whenever the piston is cocked.) There are even
electrically powered spring guns capable of full auto fire which
dominate the sport.
These airsoft guns don't fire projectiles as heavy as a small battery,
but there's no inherent reason why they couldn't be scaled up.
However, a compressed air repeater would be a better idea. It's
trivially easy to set up a main resevoir with a small leak into
the main chamber to allow multiple shots before recharging.
This is easily capable of maybe seven or so shots in a compact
form factor (assuming PVC pipe charged via bicycle pump only to
around 80psi).
> The closest
> thing that has been built was the repeating crossbows of the distant
> past. perhaps you should concentrate your efforts in that direction.
> Repeating crossbows or stonebolts, that is.
> To reasomably extract the energy available from a single or even double
> stroke of the human arm, and convert that energy into kinetic energy in
> a projectile is easy. To have it perform its work in a useful manner is
> another thing entirely.
> Energy equal mass times velocity squared. A light mass (pellet) moving
> fast can perform more useful work as a projectile (it flies reasonably
> flat, retains some energy at impact) than a heavy mass (battery) with
> the same amount of energy to move it(slow, arched trajectory).
"Useful work"? Get real, we're talking about shooting BATTERIES.
This is strictly for fun. Personally, I favor blunt paper darts
for PVC airgun projectiles. They're lightweight and consequently
suffer a lot from drag, but they're perfect for shooting without
accidentally damaging anything. In comparison, marbles shot from
the same gun will go flatter and farther and hit harder--but they
just aren't as FUN to shoot.
Isaac Kuo
Isaac Kuo
> Frankly, I know that I can test a pneumatic mechanism
> to a safe enough level (via hydraulic pressure) to make myself feel
> reasonably safe with it near me.
Sorry, it's late...in my other post, I read this to be the
opposite of what it actually said.
Isaac Kuo
Trevor Jones
cannot scale up the strength of the spring proportionally. Compare the
effort to cock the spring that projects a 1/4 gram of airsoft pellet,
and imagine scaling that up by the factor proportional to the weight of
that small battery. Tough to cock.
In this context, useful work means pretty much that it will launch it's
projectile a reasonable distance in more or less a predictable way.
Making a device that will plunk batteries out the muzzle to have them
land at your feet, does not seem to me to be performing useful work.
This is what I meant by that term.
I think Pneumatic is the real option for something like this. The
original poster might be better off with a slingshot.
Cheers
Trevor Jones
Isaac Kuo
> Isaac Kuo wrote:
>>Well, as far as the practicality of a spring gun repeater goes, there
>>are plenty of so called "single-shot" airsoft guns. (They're called
>>"single-shot" within the sport, but they're actually repeaters that
>>feed from a magazine whenever the piston is cocked.)
>>These airsoft guns don't fire projectiles as heavy as a small battery,
>>but there's no inherent reason why they couldn't be scaled up.
>The inherent reason that they could not be scaled up well is that you
>cannot scale up the strength of the spring proportionally. Compare the
>effort to cock the spring that projects a 1/4 gram of airsoft pellet,
>and imagine scaling that up by the factor proportional to the weight of
>that small battery. Tough to cock.
Tougher to cock than an airsoft, but airsoft starts off with
a pretty small force over a very short distance. There isn't
even a need for the mechanical advantage of a lever (typical
in pellet airguns, of course).
> > "Useful work"? Get real, we're talking about shooting BATTERIES.
> > This is strictly for fun.
> In this context, useful work means pretty much that it will launch it's
> projectile a reasonable distance in more or less a predictable way.
> Making a device that will plunk batteries out the muzzle to have them
> land at your feet, does not seem to me to be performing useful work.
> This is what I meant by that term.
Sure, but...
> I think Pneumatic is the real option for something like this. The
> original poster might be better off with a slingshot.
A properly designed spring piston gun would be comparable
in overall efficiency to a slingshot--and possibly a bit more
efficient. With such a heavy projectile moving at a relatively
low speed, losses are low all around for either method.
However, a spring piston gun is not easy to properly design.
The spring strength, spring length, travel distance, piston
area, projectile diameter, projectile mass, piston mass,
barrel length, etc all factor in with each other in nontrivial
interdependent ways.
There are much fewer factors to worry about with a compressed
air pneumatic, and they're very forgiving about rough guesstimates.
That said, a compressed air pneumatic is inherently less
efficient. From the moment you start compressing air into
the chamber (or resevoir), you start losing energy as the
compressed air cools down. The act of compressing a gas heats
it up, but if that gas is allowed to cool down it loses pressure
and thus potential energy. It's inevitable that the gas will
lose heat to the surrounding chamber walls (and ultimately to
the surrounding environment). In a spring piston gun, this
loss is miniscule because the compressed gas isn't given much
time to cool. In a compressed air gun, this loss is significant
because there's a good deal of time between compressing the
gas and releasing it upon firing.
Isaac Kuo
#MK
an interplexing subspace beacon on subspace frequency
> Actually, a compressed air gun pumped via bicycle pump is safer
> than a spring gun. With a bicycle pump, you don't need a safety
> valve at all--you're simply not going to be able to physically
> pump much more than 80psi or so. You'll use schedule 40 PVC
> pipe rated at well over six times that much!
>
Ahh, I always thought these were more dangerous in case you pump too much
air into it. But I see your point.
In the spring piston design, if there was too much pressure, wouldn't the
spring and piston stop halfway if the pellet fails to leave, enabling you
to drop it to the floor, crack open a side door or something and allow the
air to escape?
I.e. the gun itself shouldn't blow up? Also, couldn't a safety valve be
incorporate quite close to the pellet [but behind it and in front of the
spring] to enable too much air to leak out???
Nevertheless, thanks for your response, and the quite useful link!
Trevor Jones
Leakage will be a far harder hurdle to surpass. There IS temperature
rise on compression, and there IS cooling once the air is in the
reservoir, but it is a small portion of the energy stored. At the end of
it all, you are still storing a far greater amount of energy than you
could store via a spring, which would require that you were able to
store the energy in one stroke or perhaps more, but that gets back to
pumping, pretty much doing away with any advantage of designing a
reapeating action.
One way or another, you will NOT get more energy out than you put in.
Cheers
Trevor Jones
> Isaac Kuo
#MK
communciation via an interplexing subspace beacon on subspace frequency
> Read it where? The bow acts in a physically direct manner on the
> arrow.
> A springer deals with drag and friction while compressing the air,
> then the gas flow dynamics while moving the projectile from a standing
> start and down the barrel (more friction and drag).
>
Ahh, so I am wrong. K.
> Energy equal mass times velocity squared. A light mass (pellet)
> moving
> fast can perform more useful work as a projectile (it flies reasonably
> flat, retains some energy at impact) than a heavy mass (battery) with
> the same amount of energy to move it(slow, arched trajectory).
>
Actually 1/2m*v^2. But I get your point. Thanks.
Thanks for your points... quite useful....
Stupid idea, eh? Hehe.
AnonBloke
2003
> Well, as far as the practicality of a spring gun repeater goes, there
> are plenty of so called "single-shot" airsoft guns. (They're called
> "single-shot" within the sport, but they're actually repeaters that
> feed from a magazine whenever the piston is cocked.) There are even
> electrically powered spring guns capable of full auto fire which
> dominate the sport.
Incidentally, I did not mean an automatic thingy... I intended to cock the
gun after each shot. I was just wondering if the pellets [yeah, batteries
hehe, too heavy] could be auto-loaded. I guess it could via a magazine type
system.
Thanks again.
jkfgkjfgkjfkgj
communciation via an interplexing subspace beacon on subspace frequency
> One way or another, you will NOT get more energy out than you put in.
That would violate the law of thermodynamics!
Hmpf!
Isaac Kuo
> Isaac Kuo wrote:
> > A properly designed spring piston gun would be comparable
> > in overall efficiency to a slingshot--and possibly a bit more
> > efficient. With such a heavy projectile moving at a relatively
> > low speed, losses are low all around for either method.
[...]
> > That said, a compressed air pneumatic is inherently less
> > efficient. From the moment you start compressing air into
> > the chamber (or resevoir), you start losing energy as the
> > compressed air cools down.[...]In a spring piston gun, this
> > loss is miniscule because the compressed gas isn't given much
> > time to cool. In a compressed air gun, this loss is significant
> > because there's a good deal of time between compressing the
> > gas and releasing it upon firing.
> In reality, there seems to be no severe problem with the PCP guns.
This is because efficiency isn't the limiting factor.
> Leakage will be a far harder hurdle to surpass. There IS temperature
> rise on compression, and there IS cooling once the air is in the
> reservoir, but it is a small portion of the energy stored. At the end of
> it all, you are still storing a far greater amount of energy than you
> could store via a spring,
Yes...
> which would require that you were able to
> store the energy in one stroke or perhaps more, but that gets back to
> pumping, pretty much doing away with any advantage of designing a
> reapeating action.
...but not for that reason or anything to do with that.
The reason compressed gas guns are able to store a far greater
amount of energy than you could via a spring is simply because
gas is very light and even with the much heavier mass of the
tank you get more potential energy, pound for pound, than you
do with a spring.
For airguns, the overall weight/cost of the gun is often more
important than energy efficiency.
Isaac Kuo
Isaac Kuo
> Trevor Jones <t.o....@sympatico.ca> transmitted the following
> communciation via an interplexing subspace beacon on subspace frequency
> news:3F3046B1...@sympatico.ca on stardate 06 Aug 2003
> > Read it where? The bow acts in a physically direct manner on the
> > arrow.
> > A springer deals with drag and friction while compressing the air,
> > then the gas flow dynamics while moving the projectile from a standing
> > start and down the barrel (more friction and drag).
> Ahh, so I am wrong. K.
You're not wrong. There's no bow in the world which can hope to
compete with a springer when it comes to launching something as
light as an airgun pellet.
A springer does deal with drag and friction and gas flow dynamics,
but so does any bow (well, maybe not a bow in a vaccuum powered by
frictionless magnets).
Isaac Kuo
Isaac Kuo
> mec...@yahoo.com (Isaac Kuo) transmitted the following communciation via
> an interplexing subspace beacon on subspace frequency
> news:acc26c07.0308...@posting.google.com on stardate 06 Aug 2003
> > Actually, a compressed air gun pumped via bicycle pump is safer
> > than a spring gun. With a bicycle pump, you don't need a safety
> > valve at all--you're simply not going to be able to physically
> > pump much more than 80psi or so. You'll use schedule 40 PVC
> > pipe rated at well over six times that much!
> Ahh, I always thought these were more dangerous in case you pump too much
> air into it. But I see your point.
This can be a risk if you use a high pressure air source.
> In the spring piston design, if there was too much pressure, wouldn't the
> spring and piston stop halfway if the pellet fails to leave, enabling you
> to drop it to the floor, crack open a side door or something and allow the
> air to escape?
In any gas gun design, if there's too much pressure the gun will
fail in a way which leaks out the gas (could be anything from a
simple crack to a spectacular explosion).
The key question is whether or not "too much pressure" can happen
in the first place. With a spring piston design, the only way to
figure out the maximum pressure it might attain is with physical
testing and/or easy to mess up calculations (based on spring
strength, length, piston weight, etc...).
> I.e. the gun itself shouldn't blow up? Also, couldn't a safety valve be
> incorporate quite close to the pellet [but behind it and in front of the
> spring] to enable too much air to leak out???
You can make a weak spot on purpose to try to relieve pressure
just in case. This can be used as a safety feature on other
airgun mechanisms also.
Isaac Kuo
Trevor Jones
> ...but not for that reason or anything to do with that.
>
> The reason compressed gas guns are able to store a far greater
> amount of energy than you could via a spring is simply because
> gas is very light and even with the much heavier mass of the
> tank you get more potential energy, pound for pound, than you
> do with a spring.
>
> For airguns, the overall weight/cost of the gun is often more
> important than energy efficiency.
>
> Isaac Kuo
Yup!
For all intents and purposes, there is not any practical way to design
a spring piston airgun capable of launching batteries larger than, say,
watch batteries, with any degree of usefulness. Not in a form that could
be carried about the yard with any level of practicality, anyway. Any
projectile launcher incapable of launching it's projectile further than
the ends of the operators toes, really does not seem worth the effort.
As the original poster stated his intent to build a spring piston
airgun to launch small batteries...by which I presumed him to mean used
alkaline cells from his houshold...thus the conversations about energy
in vs. energy out and the finite limits of the human arm as a mechanism
to provide the enrgy in one or two strokes (I mention multiple strokes
because it was done on a springer. It was not a commercial
success,adding complication and wear items to the mechanism)
Cheers
Trevor Jones
Trevor Jones
> Actually 1/2m*v^2. But I get your point. Thanks.
>
> Thanks for your points... quite useful....
> Stupid idea, eh? Hehe.
Not stupid, but really impractical for a lot of reasons.
Cheers
Trevor Jones
Joseph Oberlander
> The reason compressed gas guns are able to store a far greater
> amount of energy than you could via a spring is simply because
> gas is very light and even with the much heavier mass of the
> tank you get more potential energy, pound for pound, than you
> do with a spring.
Not only that, but with HPA type systems so prevalent in paintball,
it is relatively simple to safely build 3000 PSI components into
a functional design. The hoses, connectors, tanks, and the pumps
are all rated and tested to be safe - so that's a huge part of the
equation right there as far as safety goes.
Isaac Kuo
>Isaac Kuo wrote:
>>...but not for that reason or anything to do with that.
>>The reason compressed gas guns are able to store a far greater
>>amount of energy than you could via a spring is simply because
>>gas is very light and even with the much heavier mass of the
>>tank you get more potential energy, pound for pound, than you
>>do with a spring.
>>For airguns, the overall weight/cost of the gun is often more
>>important than energy efficiency.
> Yup!
> For all intents and purposes, there is not any practical way
>to design a spring piston airgun capable of launching batteries
>larger than, say, watch batteries, with any degree of usefulness.
>Not in a form that could be carried about the yard with any
>level of practicality, anyway. Any projectile launcher incapable
>of launching it's projectile further than the ends of the
>operators toes, really does not seem worth the effort.
Pound for pound, a steel spring can still store more energy
than a slingshot's rubber (one of the possibilities
you mention as practical). The overall weight for a spring
piston airgun would be similar to a steel crossbow (another
possibility you mention as practical). A crossbow, of
course, includes a bunch of things which a slingshot
doesn't, like some sort of stock and a trigger release
mechanism, and a slitted barrel (for shooting a ball, or
in this case a battery).
> As the original poster stated his intent to build a spring piston
>airgun to launch small batteries...by which I presumed him to mean used
>alkaline cells from his houshold...thus the conversations about energy
>in vs. energy out and the finite limits of the human arm as a mechanism
>to provide the enrgy in one or two strokes (I mention multiple strokes
>because it was done on a springer. It was not a commercial
>success,adding complication and wear items to the mechanism)
But you seem to think a slingshot or a longbow would have
sufficient energy--and those involve a single stroke well
within human capabilities.
Playing with an old toy crossbow, only a few pounds of
draw over less than a foot is enough to send a AA battery
flying across a room. You can even send a AA battery across
the room with a thick rubber band! In terms of raw foot
pounds, it's a fraction of your typical spring air rifle.
If you think about it, it should be obvious you can get
a decent velocity out of a single stroke--consider the
simple act of throwing. Even without any mechanical
assistance, a single stroke is enough to get something
the weight of a baseball from the pitcher's mound to home
plate on a somewhat flat trajectory. A AA battery isn't
so heavy.
Isaac Kuo
Trevor Jones
Slingshots and bows both have long periods of time (relatively, anyway)
to act on their respective projectiles, and as a result, are quite
efficient at transfering energy within limits.
A spring piston airgun is only really effective with a relatively
lightwieght projectile
>
> > As the original poster stated his intent to build a spring piston
> >airgun to launch small batteries...by which I presumed him to mean used
> >alkaline cells from his houshold...thus the conversations about energy
> >in vs. energy out and the finite limits of the human arm as a mechanism
> >to provide the enrgy in one or two strokes (I mention multiple strokes
> >because it was done on a springer. It was not a commercial
> >success,adding complication and wear items to the mechanism)
>
> But you seem to think a slingshot or a longbow would have
> sufficient energy--and those involve a single stroke well
> within human capabilities.
It is reasonably easy to demonstrate this in a practical way. Whiz a
battery at the back fence with a slingshot. Shoot an arrow of the same
weight as a battery against said fence with a bow that has an equal draw
weight to the slingshot.
And keep in mind that a decent bow should give you 75-100 ft-lbs of
energy with a prjectile like that.
>
> Playing with an old toy crossbow, only a few pounds of
> draw over less than a foot is enough to send a AA battery
> flying across a room. You can even send a AA battery across
> the room with a thick rubber band! In terms of raw foot
> pounds, it's a fraction of your typical spring air rifle.
>
Then load up your airgun with a pellet that weighs as much as the
battery and see if it clears the barrel. My nickel says it will NOT. As
a simple test, try loading two pellets, then three and so on. Even if
you take the time to roll the extra ones so as to reduce the starting
friction by reducing their diameter, you soon reach a point where you
are better off throwing the pellets by hand. The energy transfers, but
not in a manner efficiently enough to do the work required, ie: shoot
across a yard.
> If you think about it, it should be obvious you can get
> a decent velocity out of a single stroke--consider the
> simple act of throwing. Even without any mechanical
> assistance, a single stroke is enough to get something
> the weight of a baseball from the pitcher's mound to home
> plate on a somewhat flat trajectory. A AA battery isn't
> so heavy.
>
An AA cell IS heavy. 23 grams. That's barely under 355 grains. Compared
to a .22 cal pellet at 14.3 grains, it's positively huge. At 650 fps
(713 miles per hour) the pellet has 13.4 ft-lbs of energy and is moving
at a substantial speed. To get the same energy out of the 355 grain
battery you have to move it at 130.5 fps about 88 or so miles per hour.
You should be able to throw it as fast or faster. to get the same 13.4
ft-lbs out of a .177 it has to be moving a 6.5 grain pellet at 965 fps.
And this assumes that you CAN get the battery moving effectively with a
springer powerplant.
Given that another poster has just asked how to manage to cock his 1000
fps .177 cal airgun..... I beleive it makes a bit of my point that there
is a limit to reasonable levels of power in useable, useful form,
springers-wise.
Think about it some more. There are a pile of variables that all have
complex interrelationships. Most of the cause and effect are not
immediately obvious. It should be obvious, but is not.
My reference points
http://www.beeman.com/pellcomp.htm
http://www.airguns.net/calculators.html
http://www.batterycountry.com/ShopSite/alkaline-batteries.html
Cheers
Trevor Jones
Neon John
>Hi!
>based air rifle?? [based on human power??] Preferably auto-loading?
>
>I'm just thinking of designing a cheapo, for fun gun with a cheapo
>spring, home made magazine of cheapo pellets like say, old batteries
>[mebbe too heavy] etc.
nationally recognized custom gun 'smith named Nial Tuevell, located in
Atlanta. Based on that experience, if you don't have a mill and a
lathe as a minimum setup, and you don't have any prior 'smithing
experience, I'm afraid this goal will be unreachable.
May I suggest something else that is just as much fun as shooting a
low quality air gun. A spud gun. Here's mine.
http://www.neon-john.com/Boom/Spudzooka/Spud_home.htm
This is a gun that can be built using hand tools and materials from a
big box store.
There is a group of about 50 scofflaws that have been together since
Unix mailx and long before the Arpanet went public. We call ourselves
Fanglers and we a get-together somewhere in the US every couple of
years. These are called LFBs (Low Fanglers Ball). Each LFB has a
destructive theme. One year is was to see who could do the best job
exploding vacuum cleaner (suck up a little gasoline and stand back :-)
Another LFB involved a competition to see who could build the fastest
spud gun.
I won with my Purple Pounder. It propelled a half-pound spud to over
350 fps through an Oehler chrono. After reinforcing the combustion
chamber and further optimizing the air-fuel ratio, I reached over 400
fps with a 3/4 lb spud.
The guy who was giving me some serious competition had built a
PCP-based air gun. Unfortunately the portable air compressor he was
using to pump up his PVC reservoir to 200 psi emitted an oil mist. The
oil weakened the PVC and during the championship round, the reservoir
exploded while being pressurized.
Bringing this back around to air guns, he used a common underground
lawn sprinkler pilot-operated flapper valve. This type of valve has a
solenoid that switches a small stream of water (the pilot stream) and
this stream opened the approx 1.5" main valve instantly. To modify
for air gun use, remove the solenoid and replace it with a brass
nipple attached to some plastic tubing. The gun fires when the
pressure is released.
He had rigged up a pretty decent trigger. The trigger pressed on the
shaft of a small snap-open air valve. I think he got it from
McMaster.
One note on my spud gun. After seeing the chrono readout, I became
concerned with the pressure in the combustion chamber. I rigged the
chambers with strain gauges and found far too much expansion of the
foam-core 4" PVC pipe. Based on that I wrapped both sections with
piano wire with turns as close together as possible and then soldered
the wire into solid pieces with the PVC filled with water.
I had long ago purchased a WWII-vintage aviation breathing air tank
that used the same construction. The steel tank was thinner than a
throw-away propane tank. Wire gauge was about 16 gauge. After
winding, the whole assembly had been immersed in a solder pot. The
nameplate on the tank said it was rated at 5000 psi!
So give a spud gun some thought. A PCP based unit (using something
stronger than PVC for the reservoir!) could be built in a couple of
evenings. I'd probably use copper tubing with the joints either
silver-soldered or Sil-Phos brazed together. Larger diameter copper
tubing can be had from McMasters.
I've had more fun with the Purple Pounder than with any of my firearms
or air guns. Especially at parties. The ammo is dirt-cheap and
available from any grocery store.
John
John DeArmond
http://www.neon-john.com
http://www.tnduction.com
Tellico Plains, Occupied TN
See website for email address