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Why I believe coaxials are opposite of what is best fps etc.

Post questions and info about pneumatic (compressed gas) powered cannons here. This includes discussion about valves, pipe types, compressors, alternate gas setups, and anything else relevant.
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Unread postAuthor: boyntonstu » Sat Apr 10, 2010 9:20 am

Gippeto wrote:
Gippeto wrote:Stu, if you want to compare the two layouts (co-ax vs tee), you must as you say...compare apples to apples. Hampering one or the other isn't a reasonable comparison.

New situation;

BOTH have the same chamber VOLUME and barrel.

BOTH use the same pressure and projectile.

Given these EVENLY MATCHED variables, why do you think the tee piston would produce higher fps and fpe?


The new bit.

It's been modeled, should be proof enough I'm thinking.

Would like to get to the bottom of your reasoning Stu.



This is a good discussion for many reasons.

Let's go on a bit.

What is the average size hand held rifle chamber diameter?

My guess is 1" for the chamber and obviously less for the internal barrel.


Using these two pieces of 'apples', what is the most efficient use of them to create an air cannon?

Build a coax with the smaller barrel or use the 1" tube as the barrel?

If we restrict the question to using these 2 pieces of tubing, my contention is not to build a coax.
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Unread postAuthor: Ragnarok » Sat Apr 10, 2010 9:55 am

What you're doing with that above post is creating a loaded question that you know hampers the coaxial more.

Forget a fixed chamber diameter. For this to be a fair discussion with any point to it, we need to be talking about fixed barrel dimensions (in this case, 3/4" Type L copper, 38" long), with a chamber chosen as appropriate to each launcher.

And I have already demonstrated that it is perfectly practical to build a 600 psi coaxial around that barrel, and one that will offer very respectable performance.

To say that a coaxial is unable to support a barrel as big as its chamber diameter... Well, no s***, Sherlock!
What you're doing is taking the integral fact of a launcher, then saying that a launcher is useless for all other purposes because it can't do that one thing.

I might as well be listening to this conversation:

Lord Clive Ponsonby-Smallpiece: I say Blenkinsop, can one transport a flaming pink elephant in a British Leyland Mini?
Sir Charles Andrew Blenkinsop the 4th: No, sire, I dare say that a British Leyland Mini is not possessed of sufficient internal volume for one to fit a pacyhderm within.
Lord Clive Ponsonby-Smallpiece: What? (Monocle flies off in surprise) Well then, sirrah, a British Leyland Mini is clearly of no use at all.

And that as a discussion point ignores the fact that a Mini, as a car, while it cannot transport something as big as an elephant, is still a perfectly viable transport for people (well, provided they're not too fat).

Now take that above paragraph, replace the word "Mini" with "coaxial", "car" with "launcher", "transport" with "support", "an Elephant" with "a chamber diameter barrel" and "people" with "a smaller barrel". You'll get this:

And that as a discussion point ignores the fact that a coaxial, as a launcher, while it cannot support something as big as a chamber diameter barrel, is still a perfectly viable support for a smaller barrel.

You can't say "Well, it's no good for what I want to do, so it's no good for anyone else either".
If you need to transport an elephant, don't use a Mini. But you can't say that because something isn't right for your job that it's not right for someone else's.
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Unread postAuthor: al-xg » Sat Apr 10, 2010 10:25 am

Build a coax with the smaller barrel or use the 1" tube as the barrel?


But in that case the T piston would also require larger tube, or a larger T to house the piston, so its really just a question of how much of that tube you want to use, but you'll still be using it. I really don't see coaxials as being radically different; its just chamber positioning, like having a T piston valve with a 90 then two 45 degree angles and having a separate coaxial chamber(which has been done a few times I believe).

The best efficiency (projectile energy vs energy stored in chamber) will come with the valve with the better flow. Diameter and pressure will come into that but also turbulence and friction losses due to shapes surfaces angles inside the valves.

The most efficient set up in my opinion (or that I can think of at the moment) would be an inline coaxial (chamber behind barrel and long piston, no internal barrel) with an aerodynamically profiled piston so that the flow would be as smooth and unobstructed as possible, maybe even have some sort of rifled chamber or using angled blades to get the fluid rotating.
For practical reasons one might put up with one elbow, not even maybe as steep as 90 degrees, to accommodate a loading mechanism or something.
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Last edited by al-xg on Sat Apr 10, 2010 10:43 am, edited 3 times in total.
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Unread postAuthor: boyntonstu » Sat Apr 10, 2010 10:27 am

Ragnarok wrote:What you're doing with that above post is creating a loaded question that you know hampers the coaxial more.

Forget a fixed chamber diameter. For this to be a fair discussion with any point to it, we need to be talking about fixed barrel dimensions (in this case, 3/4" Type L copper, 38" long), with a chamber chosen as appropriate to each launcher.

And I have already demonstrated that it is perfectly practical to build a 600 psi coaxial around that barrel, and one that will offer very respectable performance.

To say that a coaxial is unable to support a barrel as big as its chamber diameter... Well, no s***, Sherlock!
What you're doing is taking the integral fact of a launcher, then saying that a launcher is useless for all other purposes because it can't do that one thing.

I might as well be listening to this conversation:

Lord Clive Ponsonby-Smallpiece: I say Blenkinsop, can one transport a flaming pink elephant in a British Leyland Mini?
Sir Charles Andrew Blenkinsop the 4th: No, sire, I dare say that a British Leyland Mini is not possessed of sufficient internal volume for one to fit a pacyhderm within.
Lord Clive Ponsonby-Smallpiece: What? (Monocle flies off in surprise) Well then, sirrah, a British Leyland Mini is clearly of no use at all.

And that as a discussion point ignores the fact that a Mini, as a car, while it cannot transport something as big as an elephant, is still a perfectly viable transport for people (well, provided they're not too fat).

Now take that above paragraph, replace the word "Mini" with "coaxial", "car" with "launcher", "transport" with "support", "an Elephant" with "a chamber diameter barrel" and "people" with "a smaller barrel". You'll get this:

And that as a discussion point ignores the fact that a coaxial, as a launcher, while it cannot support something as big as a chamber diameter barrel, is still a perfectly viable support for a smaller barrel.

You can't say "Well, it's no good for what I want to do, so it's no good for anyone else either".
If you need to transport an elephant, don't use a Mini. But you can't say that because something isn't right for your job that it's not right for someone else's.



How do we go about designing a gun?

Do we choose the external shape first or the barrel size?

Another point is whether you wish to breech load or muzzle load.

Can you breech load an arrow into a coax?

If the performances were equal for the same size envelope (they aren't), I would go for the breech loader.

If I wished to shoot 10 gauge shotshell hull darts about 6" long that fit perfectly inside a 3/4" L barrel, I can't see building a coax.

BoyntonStu
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Unread postAuthor: Crna Legija » Sat Apr 10, 2010 10:33 am

if the piston is serviceable than you could breech load a arrow :D
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Last edited by Crna Legija on Sat Apr 10, 2010 10:40 am, edited 1 time in total.
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Unread postAuthor: al-xg » Sat Apr 10, 2010 10:36 am

Can you breech load an arrow into a coax?

You'd need a massive breech with either option, maybe easier to build with a T, but in my opinion it is easier still to muzzle load something like an arrow.

And in fact a coaxial of the same barrel diameter would probably be more compact, but in 3D (using the available volume in every direction instead of just in one).
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Unread postAuthor: Ragnarok » Sat Apr 10, 2010 10:50 am

AGAIN, PLEASE STOP QUOTING MY ENTIRE POSTS.

boyntonstu wrote:How do we go about designing a gun? Do we choose the external shape first or the barrel size?

Depends on the person, obviously. Some people will design a launcher because it'll fire a certain projectile, some because it will be a nice shoulder fired cannon, some because it'll fit in a pocket, etc, etc.

Another point is whether you wish to breech load or muzzle load.

Completely irrelevant to the discussion. The discussion is about velocity, not whether or not the launcher can be loaded in a certain way.

To start talking about another problem behind a coaxial when the subject is velocity is a case of the logical fallacy known as Ignoratio elenchi. Your arguments are valid in of themselves, but not relevant to the discussion, and therefore just a waste of everyone's time.

~~~~~

I'm trying to avoid interpreting this topic as you just not liking coaxials, starting on one point, then just progressing on to non-sequiturs now the original argument has been called into contention. But that's not exactly a easy thing for me to avoid with the way you're acting.

We can either get back to the appropriate subject - that subject being the relative velocities of co-axial launchers and barrel sealing launchers on a fair "apples with apples" playing field - or we can call it off because that's no longer what you're trying to discuss.
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Unread postAuthor: velocity3x » Sat Apr 10, 2010 10:59 am

boyntonstu wrote:How do we go about designing a gun?

Function followed by form.
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Unread postAuthor: Moonbogg » Sat Apr 10, 2010 11:30 am

velocity3x wrote:
boyntonstu wrote:How do we go about designing a gun?

Function followed by form.


Right. You just pick what you want it to do, then make it accordingly. However, if you want something small for portability, then form might be the first priority, but then again form itself becomes the function then and you would try then to get the most out of that size and shape. In other words man, I don't friggin know! Thats a wierd question. Some people don't design at all. They just pick some materials and make the thing. Nothing wrong with that! (usually)
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Unread postAuthor: boyntonstu » Sat Apr 10, 2010 12:13 pm

Ragnarok wrote:AGAIN, PLEASE STOP QUOTING MY ENTIRE POSTS.

boyntonstu wrote:How do we go about designing a gun? Do we choose the external shape first or the barrel size?

Depends on the person, obviously. Some people will design a launcher because it'll fire a certain projectile, some because it will be a nice shoulder fired cannon, some because it'll fit in a pocket, etc, etc.

Another point is whether you wish to breech load or muzzle load.

Completely irrelevant to the discussion. The discussion is about velocity, not whether or not the launcher can be loaded in a certain way.

To start talking about another problem behind a coaxial when the subject is velocity is a case of the logical fallacy known as Ignoratio elenchi. Your arguments are valid in of themselves, but not relevant to the discussion, and therefore just a waste of everyone's time.

~~~~~

I'm trying to avoid interpreting this topic as you just not liking coaxials, starting on one point, then just progressing on to non-sequiturs now the original argument has been called into contention. But that's not exactly a easy thing for me to avoid with the way you're acting.

We can either get back to the appropriate subject - that subject being the relative velocities of co-axial launchers and barrel sealing launchers on a fair "apples with apples" playing field - or we can call it off because that's no longer what you're trying to discuss.



I agree with you that I added an element, breech loading, simply because I just thought about it this morning.

The question is apples for apples.

If you feed a 3/4' barrel with a 1" chamber is that comparable to feeding a 1" barrel with a 3/4" chamber?

What makes the Apple an Apple?

Again, the OP was not limited to fps.

Please read it again.

"If you wish to throw away force, acceleration, and fps, build a coax. "
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Unread postAuthor: velocity3x » Sat Apr 10, 2010 12:45 pm

boyntonstu wrote:What makes the Apple an Apple?


Ummm...Genetics???
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Unread postAuthor: al-xg » Sat Apr 10, 2010 4:43 pm

The apples for apples element, using apples in two barrel sizes doesn't really work.

Any change in barrel diameter is a change to the square on the surface area but a change to the cube on the volume and therefore density and weight.
So the apple bits wouldn't be the same weight.
In this case I think you'll find the smaller calibre will produce a higher velocity the larger one probably a higher muzzle energy.

To make the weights equal you would have to reduce projectile length. The velocity in the larger bore will probably beat the smaller bore's but then you end up with a faster projectile with a lower sectional density.

Sectional density tends to be a good thing in most ballistic applications, as it means that a projectile of the same weight will be less affected by drag, other turbulence such as wind and muzzle blast, (friction on penetration of the target...) etc... And that is mostly because of the frontal area versus mass. As an example: acceleration=force/mass, and with say aerodynamic drag,(D=1/2*fluid density*Area*velocity^2*drag coefficient),a larger area makes a higher drag force and a larger force with a constant mass will result in higher acceleration or in this case deceleration for the projectile. Oh and notice that velocity is squared.

So that larger bore projectile, although it has a higher muzzle velocity, will slow down much sooner and have less range, and be more likely sent off trajectory by winds, muzzle blast etc... Not a good thing most of the time.
Then again depending on the exact shape and size of the projectile the shorter one might end up being more stable in flight if it tumbles.

But basically it depends on how large the picture is when efficiency is compared. But that is internal and external ballistics, user ergonomics have also been mentioned, one could expand the matter quite far as long as people are comparing the same things.

boyonstu wrote:
Ragnarok wrote:AGAIN, PLEASE STOP QUOTING MY ENTIRE POSTS.
Brilliant :)
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Unread postAuthor: Ragnarok » Sat Apr 10, 2010 6:36 pm

boyntonstu wrote:
Ragnarok wrote:AGAIN, PLEASE STOP QUOTING MY ENTIRE POSTS.

Seriously. :roll:

BoyntonStu - Please, stop it. There has been absolutely no need in any of these cases to quote the entire posts. A couple of lines from most of them would have been more than sufficient.

If you don't feel up to cutting down the posts to just the relevant parts, then please go for the "@Ragnarok" approach.
But actually just cutting down a post as appropriate is no great challenge. Observe, as I demonstrate the skill below:

~~~~~

I agree with you that I added an element, breech loading, simply because I just thought about it this morning.

So you are just on a coaxial bashing rant?

We didn't need a topic for you to tell us why you don't like a certain kind of cannon, just like we don't need a topic for me to say why I don't build hybrids. If everyone made a topic to say "I don't like marbles as ammunition" or "I think QEVs are the mutt's nuts", we'd have a lot of very pointless topics.

Telling us something new and relevant to us is fine. If you can conclusively tell us why a co-axial sacrifices a notable amount of performance in an apples to apples situation - which I am taking as the chamber volume being identical, the pressure being identical and the barrel being identical, then you've got a discussion that's worth having.

The fact that coaxials can't be easily breech-loaded is not news. Unless you have an advancement to make on that fact, then there's no point in discussing it.

If all you're here to do is tell us you don't like something... well, whoopdedoo. Nobody likes everything. You've got your reasons for not liking it. Other people have their reasons for liking it. You can't say your reasons are right for them.

"If you wish to throw away force, acceleration, and fps, build a coax. "

Your point being? Velocity is the integral of the acceleration with respect to time and acceleration is directly proportional to force. And, although you didn't originally mention it, energy is the integral of force with respect to distance.

They are all inherently linked. And for a projectile of a given mass in a barrel of given dimensions ("apples to apples", remember), they are all related to each other by a strict mathematical relationship.

So, under our apples to apples discussion, if one changes, all the others will change in kind, according to the laws of motion.

Can force, acceleration, velocity and energy change when you've got a given barrel, chamber volume, pressure and projectile? Of course - take GGDT, take any cannon, then halve the valve flow coefficient.

Less air flowing through the valve, less pressure, less force, less acceleration, less velocity, less energy.

Basically, what this discussion comes down to is "Can you conclusively say that a coaxial's valve design is less efficient than a barrel sealer's valve design, and why?"

Anything else is not an apples to apples discussion on the subject matter of force/acceleration/velocity/energy.

EDIT: Spelking mistoks.
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Unread postAuthor: POLAND_SPUD » Sat Apr 10, 2010 7:04 pm

this topic is a bit pointless for most of us but it's a good source of info for new members...
which I am taking as the chamber volume being identical, the pressure being identical and the barrel being identical, then you've got a discussion that's worth having
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Unread postAuthor: Gun Freak » Sat Apr 10, 2010 7:08 pm

Ohhh POLAND doubled... :shock: haha
Yeah I'm folowing this thread, and even though Rag's posts are incredibly long, I read them for the good info and I would love to see where this will end... if it ever does... but anyway I really would like to know if there is any difference when comparing apples to apples a tee piston vs a co-ax, because I want to build each of those pretty soon.
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