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Co-axial barrel options

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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Co-axial barrel options

Unread postAuthor: trigun » Mon Feb 16, 2009 9:18 pm

I am building my Co-axial. So far i have 6' feet of 4" inch sch.40. Am i trying to decide on a 1.5" inch barrel or a 2" barrel. Opinions on that one please.
Then i see that many of the co-ax cannons use male to female adapters to make there pistons service able. Will using 4" male/ female combo work under pressure ? I am worried it will not withstand the force of the pressure and the piston.
I ask this because i didn't see any large 4" chamber co-ax piston cannons that had the serviceable male/female combo. Would i have to instead dremel a O-ring on a bushing and screw that in.
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Unread postAuthor: starman » Mon Feb 16, 2009 10:22 pm

I'm a little biased here but I think golf ball ammo is the bomb. No, it's not perfect by any stretch but it's pretty darned good and readily available. That means an SDR 21 1.5" barrel. 2" isn't good for much beyond big potatos or specialized homemade ammo.

I think you'll be OK with the 4" if you use pressure rated parts. If use 1.5" barrel you might even consider stepping down to 3" at the piston...makes for much less force on the piston and those rear parts....and you'll still have plenty of flow for the 1.5" barrel.
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Unread postAuthor: trigun » Mon Feb 16, 2009 10:29 pm

Ok thanks starman, I have lots of 4" laying around so I'll probally stay with that though. As for the barrel getting sdr-21 is a big %$# so i could always go 2" then somehow put sdr-21 in it if a got some. Maybe I'll check yellow pages for plumbing supply. Yes I always use pressure rated parts now why I never posted my second cannon on here it has lots of dwv and I would get flamed horribly.

Took a look at your co-axial I get what your saying

Edit 2.0 would 4" at 180 psi or 3" at 240 be more powerful
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Unread postAuthor: jook13 » Mon Feb 16, 2009 10:44 pm

If you get 2 inch with the plans of putting 1.5 sdr in later, make sure you get 2 inch shcedule 80. The sdr wont fit in the schedule 40 with cutting a piece out. I have to agree with starman in that golfball barrells are the bomb.

I dont see any reason the threaded parts wont withstand the pressure of the piston. Just make sure you use some kind of bushing on the back of your piston to cushion the blow. I used a bushing with an o-ring because it was easier to make the pilot volume smaller, so that is something to think about as well.
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Unread postAuthor: trigun » Mon Feb 16, 2009 10:57 pm

I live next to a golf course so golf balls do dominate right now. Sorry jook.
Yea i think I'm going to use 4" and maybe make a 3" one later because my current air compressor goes to 180 psi.
So on the front is 4"-1.5" bushing
then 6 foot of 4"
male adapter on end - female 4" with 4"-1.5" reducer then my pilot
piston will be a 3" end cap
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Unread postAuthor: jeepkahn » Tue Feb 17, 2009 9:07 am

Or you could make a toolie valve chamber and have interchangeable barrels like on my modular gun... 4" by 24" chamber, and I use camlocks for the barrels, I've got a GB barrel, a 3"barrel, a 2.5" barrel, a 2" barrel, and a 1.5" barrel.....
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Unread postAuthor: trigun » Tue Feb 17, 2009 4:34 pm

I Actually want to make a co-axial piston maybe a toolie valve after the this one 8) .
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Unread postAuthor: jeepkahn » Tue Feb 17, 2009 4:58 pm

trigun wrote:I Actually want to make a co-axial piston maybe a toolie valve after the this one 8) .


checkout my posts with my golf ballcannon... Mine has a servicable piston, also you should try making a "cup" style piston so that you don't have as much weight or dead space being taken up... And you can use a spring to help cushion the piston "blowback" like JSR uses...
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Unread postAuthor: trigun » Thu Feb 19, 2009 1:15 am

well i really dont want to start a new topic on this but i keep thinking about this and how do i glue in the barrel of co-axial. I'm speaking of the front bushing not the support inside the chamber. I was thinking slide the pipe in put glue on section of barrel then push it down into the bushing to glue it ? I really dont want to waste my sdr pipe :oops: .
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Unread postAuthor: starman » Thu Feb 19, 2009 2:06 am

trigun wrote:well i really dont want to start a new topic on this but i keep thinking about this and how do i glue in the barrel of co-axial. I'm speaking of the front bushing not the support inside the chamber. I was thinking slide the pipe in put glue on section of barrel then push it down into the bushing to glue it ? I really dont want to waste my sdr pipe :oops: .


Getting a coax properly cemented IS a big challange. At least one of your joints will have to be epoxied because it doesn't cure immediately like PVC cement does...gives you a little working time. Get all your parts prepped and plan the order of your cementing and epoxying....practice it first, several times. This is important. If you mess it up you'll be starting over.
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Unread postAuthor: trigun » Thu Feb 19, 2009 4:17 pm

But is what i said correct. Slide it in partially. put glue on spot of barrel. push until glue is in joint then I'm good ? Epoxy if necessary.
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Unread postAuthor: Combustion Monkey » Thu Feb 19, 2009 4:50 pm

I have built many pass through fittings for my coaxial combustion and have never used epoxy. I find that as long as good attention is payed when modifying the fittings everything stays square ( and I am using a dremel). It is true that epoxy would increase the time for last second adjustments but if all goes well your fittings will self center. And trigun what you said is true about the glueing process. But if you are using pvc cement you have to prime the inside of the slip joint. Doing this will smear the primer down the barrel as its slid through removing primer from the joint during the process. I prime the entire length of the barrel thats passing through the fitting.This way it acts as lube and keeps all parts of the joint primed. When the peaces are almost were you want them add a good amount of cement to the area that will be glued on the barrel and slide it into place. I hope that made some sort of cense.
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Unread postAuthor: trigun » Thu Feb 19, 2009 10:57 pm

Thank you combustion monkey just wanted to make sure i was actually thinking taping the barrel but still putting primer on it. This would allow me to protect the barrel from the primer and still keep the primer coating good on the lip of the bushing. All my parts will be square as they always are haha. I love power tools and carpenter levels !
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