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A place to ask general spud cannon related questions.
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Unread postAuthor: sandman » Sat Aug 18, 2007 11:54 am

ok, hopefully today im going to get a GB barrel and i wanted it to be interchangeable, but the cannon is already built, so does anyone think it is safe to slide the barrel in w/o gluing, or will it come flying out with the projectile.

BTW, its a sprinkler valve cannon so no pressure above 125 is going to be used probably
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Unread postAuthor: jimmy101 » Sat Aug 18, 2007 12:16 pm

A little more info would be helpful. "Slide the barrel in" means what? Slide it into what? A previous barrel, a fitting, your a ...?

A golfball is about 1.6" in diameter, area=2in<sup>2</sup>. Ignoring the area of the barrel walls, you'll have (2in<sup>2</sup>)(125pounds/in<sup>2</sup>)=250 pounds of force trying to pop the barrel out of the gun. So, if you hung the gun from the cieling could you and a budy hang from the barrel without pulling it out of the gun?

It might be possible to use screws to hold the barrel in place.
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Unread postAuthor: sandman » Sat Aug 18, 2007 12:31 pm

ok, um, the current barrel 2" sch 80, i was planning to make the GB Barrel longer than the barrel and put a hole through so that i could take it out with a screwdriver

there is more discription as you requested, and um does all the force you show really apply to the barrel?
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Unread postAuthor: SpudBlaster15 » Sat Aug 18, 2007 2:03 pm

sandman wrote:and um does all the force you show really apply to the barrel?


No, that is the force applied to the barrel on Jupiter. :roll:

Most people cement the 1.5" SDR21 barrel onto the gun, then sleeve the 2" Sch 80 over top of it. If you do it the other way around and cement only the 2" Sch 80 pipe to the gun, expanding gases will leak between the pipes, and the inner pipe might just come flying off of the gun.
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Unread postAuthor: CannonCreator » Sat Aug 18, 2007 2:12 pm

Dude not a good idea. That sounds very un peredictable. Post some pics of the cannon and were you want to put on the longer barrel, and Im sure we can give you a 100% safe idea for you.
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Unread postAuthor: boilingleadbath » Sat Aug 18, 2007 3:00 pm

A golfball is 1.68"; the inside of the sdr21 is 1.7", the inside of the sch80 is 1.9".

Further, there are 4 forces acting on the sdr21:
1) The force of the air on the sdr21 pipe, equal to .78*air_pressure*(1.9<sup>2</sup> - 1.7<sup>2</sup>)
2) The frictional force of the golfball during it's travel (not very much)
3) The force required to accelerate the barrel backwards when the gun recoils, equal to .78*1.68<sup>2</sup>*air_pressure*(sdr21_mass/total_gun_mass)
4) The force of the sch80 restraining the sdr21 from shooting out.

Add up #1,#2,and #3... and remember that #4 has to be greater than that number.

(at 100 psi, we find that #1 is 56 pounds. There, saved you some math.)
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Unread postAuthor: frankrede » Sat Aug 18, 2007 4:15 pm

SpudBlaster15 wrote:
sandman wrote:and um does all the force you show really apply to the barrel?


No, that is the force applied to the barrel on Jupiter. :roll:

Most people cement the 1.5" SDR21 barrel onto the gun, then sleeve the 2" Sch 80 over top of it. If you do it the other way around and cement only the 2" Sch 80 pipe to the gun, expanding gases will leak between the pipes, and the inner pipe might just come flying off of the gun.
I usually see the gun with the 2" sch 80 that goes onto the gun/I put a bolt through both pipes and the gun seems fine.
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Unread postAuthor: Rudesill Ballistics » Thu Aug 30, 2007 1:59 am

This is one reason why I make all my guns with removable parts, so if I wanted a GB barrel, I could just make one and screw it on.

And to answer your question, GLUE GLUE GLUE!!!! The GB might decide to take your barrel sleeve along with it.
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Unread postAuthor: Novacastrian » Thu Aug 30, 2007 3:41 am

Most of my guns use a setup just as you are describing, however i have full machining facilites, you could do the same as i do in a lathe however.
I don't use "press fit" ( it's kinda like a morse taper ) on my Hybrid or Large Combustion though. The barrel would come straight off!! :P

I think you can get it to work :wink:
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