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

Unread postAuthor: boyntonstu » Fri Apr 09, 2010 11:08 am

In a coaxial, the chamber is large in diameter than the barrel.

Larger diameters are weaker than small diameters when it comes to chamber design.

The smaller the barrel/projectile the less the force on a projectile for a given pressure.

IOW A coax is working against itself design wise.

For example my Trom-Boyn uses 3/4" Copper type L for both the chamber and the barrel.

The barrel is 38" long and the chamber is effectively 17" in length.

If I changed the barrel to 1/2" Copper type L and used the same 600 psi pressure the force on a projectile would be reduced by ratio the squares of their diameters.

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

It makes zero sense to build a cannon/rifle to me unless I MUST have the most compact design to fit a small space.
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Last edited by boyntonstu on Sat Apr 10, 2010 1:20 pm, edited 2 times in total.
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Unread postAuthor: SpudBlaster15 » Fri Apr 09, 2010 11:24 am

Coaxial launchers were never designed to offer maximum performance; they were intended to provide a neat appearance and a high power to length ratio, which the coaxial design accomplishes quite effectively. Clearly, if you're looking for raw performance, an inline cannon design is best.
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Unread postAuthor: Bluetooth » Fri Apr 09, 2010 11:26 am

It's not like you often max out the pressure of the pipe anyway. if you need more strength, use stronger pipe. Coaxials look sweet, are compact, and make it easy to implement a powerful diaphragm valve. It is ypur choice if you want to make a coax or not. I personally love them.
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Unread postAuthor: Crna Legija » Fri Apr 09, 2010 11:30 am

im pretty sure coax are more powerful than barrel sealers because air come from all around the barrel than just the bottom
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Unread postAuthor: Mr.Sandman » Fri Apr 09, 2010 12:28 pm

Well that may be true but no need to put coaxials down, they have feelings to you know. :D For one thing coaxials are easier to make, cost less, and can be easily made with epoxy and whatever you have on hand. So if you are a beginner and want to make a quick piston valve then coaxials are indeed whats best. Then again everyone has their own opinion of whats best.
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Unread postAuthor: clemsonguy1125 » Fri Apr 09, 2010 1:15 pm

I agree that tee valves are better if performance is what you want but you you can't make tee valve pen guns so both have pros and cons
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Unread postAuthor: boyntonstu » Fri Apr 09, 2010 1:26 pm

-_- wrote:im pretty sure coax are more powerful than barrel sealers because air come from all around the barrel than just the bottom


I disagree.

The diameter of the barrel is the key to power, not how the compressed air feeds into it.
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Unread postAuthor: Gippeto » Fri Apr 09, 2010 1:31 pm

Well, that's a can of worms split wide open. :lol:

If we're going to start throwing opinions around...

I believe that the co-axial configuration has some advantages other than "space saving".

Consider that drag increases as the square of velocity...now think about mass flow rate. The larger volume available at the valve in a co-ax should result in lower air velocities inside the chamber...reducing drag/wasted energy, and eliminating any formation of shock waves within the chamber itself (another big waste of energy). This I believe will net out higher velocities at the muzzle. The larger the chamber diameter at the valve for a given barrel id, the greater the effect.

Wonder about the benefits of mass flow rate? Check out Techs qdv builds...they take full advantage of it. It's not just a good valve.

Without side by side builds to quantify it...it's just a theory, but one with which I'm content.

As to co-axials being low fps pieces, my own personal experience says otherwise;

http://www.spudfiles.com/forums/x-1-1-m ... 16607.html

And I have to agree with Bluetooth...if you need a stronger tube...use one. :)
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Unread postAuthor: POLAND_SPUD » Fri Apr 09, 2010 1:41 pm

I don't think you concentrate on the most important thing here... coax can't be breech loaded
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Unread postAuthor: boyntonstu » Fri Apr 09, 2010 1:44 pm

Gippeto wrote:Well, that's a can of worms split wide open. :lol:

If we're going to start throwing opinions around...

I believe that the co-axial configuration has some advantages other than "space saving".

Consider that drag increases as the square of velocity...now think about mass flow rate. The larger volume available at the valve in a co-ax should result in lower air velocities inside the chamber...reducing drag/wasted energy, and eliminating any formation of shock waves within the chamber itself (another big waste of energy). This I believe will net out higher velocities at the muzzle. The larger the chamber diameter at the valve for a given barrel id, the greater the effect.

Wonder about the benefits of mass flow rate? Check out Techs qdv builds...they take full advantage of it. It's not just a good valve.

Without side by side builds to quantify it...it's just a theory, but one with which I'm content.

As to co-axials being low fps pieces, my own personal experience says otherwise;

http://www.spudfiles.com/forums/x-1-1-m ... 16607.html

And I have to agree with Bluetooth...if you need a stronger tube...use one. :)


First, compare apple with apples.

Speed AND projectile weight have to be compared at the same pressure.

Take any coax and pull out the barrel to use as the chamber.

You automatically have a more powerful gun.


For example: Assume a coax with a chamber cross sectional area of 2 square inches and has a barrel of 1 square inch. Pump to 100 psi.

When you pull the trigger, the projectile will be hit with 100 pounds of force. 100 psi acting on 1 inch = 100 pounds of force.

Now reverse the scenario.

You pressurize the barrel to 100 psi and pull the trigger.

The projectile will be hit with 200 pounds of force with the same 100 psi of pressure. That is 100 pound PER square inch.

If the barrel had 4 square inches of area, the projectile will feel 400 pounds of force.

It is very simple, more area means more force, which means more acceleration and power.

100% positive!


BTW I am not putting down anything.

I am sharing scientific information.
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Unread postAuthor: Gippeto » Fri Apr 09, 2010 1:48 pm

How important IS rate of fire on a spuddy?

Is a busted appliance/monitor going to get up and run away if you miss with the first shot?. :wink: :lol:

Mine never have... :idea: ...maybe its the Polish appliance fairys??? :lol:


Won't double post;

Stu...the original topic was about fps...not fpe. Increasing bore size WILL increase fpe...no doubt about it.

Removing the barrel from within the chamber will increase chamber volume...this also ALWAYS has an effect on power output.
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Unread postAuthor: POLAND_SPUD » Fri Apr 09, 2010 2:13 pm

How important IS rate of fire on a spuddy
more less as much as power...


hitting
a busted appliance/monitor
once is not as cool as hitting it 10 times
you must be Canadian if you don't understand it
:D
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Unread postAuthor: boyntonstu » Fri Apr 09, 2010 2:38 pm

Gippeto wrote:How important IS rate of fire on a spuddy?

Is a busted appliance/monitor going to get up and run away if you miss with the first shot?. :wink: :lol:

Mine never have... :idea: ...maybe its the Polish appliance fairys??? :lol:


Won't double post;

Stu...the original topic was about fps...not fpe. Increasing bore size WILL increase fpe...no doubt about it.

Removing the barrel from within the chamber will increase chamber volume...this also ALWAYS has an effect on power output.




Stu...the original topic was about fps...not fpe. Increasing bore size WILL increase fpe...no doubt about it.

From the OP:

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

FPE was implied when I mentioned force, acceleration, and fps when considering the same weight projectile.

So we agree that coax's are weaker than barrel sealers of larger diameters.

BTW What coax could be easier to build than this:

¾” Pneumatic Rifle

[youtube]http://www.youtube.com/watch?v=yMtvC_0D1Ls[/youtube]
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Unread postAuthor: Mr.Sandman » Fri Apr 09, 2010 2:46 pm

Boyntonstu Also coaxials tend to have longer chambers which compensates for the lack of space. Edited for sake of clarity
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Unread postAuthor: velocity3x » Fri Apr 09, 2010 3:36 pm

boyntonstu wrote:Why I believe coaxials are opposite of what is best for fps.


A few post later you said:

The diameter of the barrel is the key to power, not how the compressed air feeds into it.


That statement conflicts with your original post. Essentially you're saying that it's a gun design issue and not a coax vs. piston issue. :?
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