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The Bettie, now with damage pics in the first post!

Built a combustion cannon? Then post it here! This section is for completed, finished cannons that you have built. Please include pictures and information.
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The Bettie, now with damage pics in the first post!

Unread postAuthor: Combustion Monkey » Sun Jan 11, 2009 8:01 pm

The gun is a coax breach loader running a 346 cubic inch chamber [ thats figuring in the barrel volume ] into a 1.5in barrel. The barrel is made in sections so it can be up to 13ft long but usually has about 3.5ft of exposed barrel for handling sake.

It is triggered by pressing the momentary switch on each grip at the same time. I have found that having a deadman switch avoids having my dog or a curious bystander from firing the gun by accident. I have found that dogs get almost as much fun from spudding as I do!

Fuel is direct propane injection with a 200k volt stun for ignition wired into a duel spark strip.

80mm cpu fan for venting and yes it lights up but i got it for free.

This is my first spud gun. It is still a work in progress, but here it is. Any thoughts that any one has would be more than welcome.

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Side views

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coax breach loading barrel

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spark strip

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chamber fan

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Some damage.

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The entrance.

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The exit.

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EDIT: fixed bad picture links
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Last edited by Combustion Monkey on Tue Feb 10, 2009 4:33 pm, edited 4 times in total.
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Unread postAuthor: jrrdw » Sun Jan 11, 2009 9:23 pm

So how well does it work? Looks bad to the bone! Nice job CM. Did you come up with this configuration on your own? Very nicely done.
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Unread postAuthor: Combustion Monkey » Sun Jan 11, 2009 9:32 pm

Yea its my design, with some wisdom from poking around on this forum. It works VERY well, the best guess at range so far is 350-400yds with the 9ft barrel. It goes bang every time and i have a cam lock setup in the works for fast barrel / caliber changes. I still need to clean up the wiring a bit before paint but that wont take long. Once the weather warms back up above freezing i hope to get some damage pics up.
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Unread postAuthor: starman » Sun Jan 11, 2009 9:36 pm

One of the few coaxial combustions on the site. I too would like to see some performance numbers.

You've done a lot with this cannon. The first thing I'll note is that you used a DWV wye connection in the middle. These aren't rated for pressure usage....although it's generally a major no-no with pressurized pneumatic gun and a "ok we'll let these one slip by" on combustion guns.

I like your handle work and the general construction looks well thought out and solid. I assume you unscrew the wye cap for fresh air and the rear "cap complex" to reload.

Nice cannon... :wink:
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Unread postAuthor: Combustion Monkey » Sun Jan 11, 2009 9:41 pm

Thats all correct Starman. I had no choice on the wye, i wanted the directional effect of the pipe sending a pressure wave rearward to the breach and needed to find a way to mount a fan in a coax. It gets checked for stress cracks regularly and no problems yet. And right on having to pop two ports to vent. The port nearest the vent may get a ball valve in the near future. Oh and it balances perfect when held by the front grip or set on the ground. Pure accident but its cool!
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Unread postAuthor: starman » Sun Jan 11, 2009 11:00 pm

Combustion Monkey wrote: i wanted the directional effect of the pipe sending a pressure wave rearward to the breach and needed to find a way to mount a fan in a coax.


Getting a fan into a coax would be an interesting challenge with standard PVC parts. I guess I hadn't given it that level of thought.

I would get a ball valve on that air inlet just for quick and convenient operation if nothing else. You could also configure a cool camlock system to get to your breech easier.
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Unread postAuthor: jook13 » Sun Jan 11, 2009 11:10 pm

I think your setup for the fan is borderline brilliant, as is the "ring" spark strip to accomidate the coax shape.

I like it, I wanna see a wicked video of you destroying something... :twisted:
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Unread postAuthor: Combustion Monkey » Mon Jan 12, 2009 6:04 pm

Thanks for the great feedback! I ordered the parts for the camlock breach today, had to go 3in, the 4in was going to cost $100 for the two parts, but designing around problems is why i do this. Also got a ball valve, but i may shelve the pvc valve for a sick unit i saw when ordering the camlock, it only weighs a bit more and i can recycle the one i have onto another gun.

Just want to say thanks again to the entire forum. This cannon is proof of what can be done on a first project when you just take a little time to research and plan.
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Unread postAuthor: inonickname » Mon Jan 12, 2009 9:36 pm

nice gun, not all new people come here displaying such ingenuity. Job well done
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Unread postAuthor: starman » Mon Jan 12, 2009 10:37 pm

Combustion Monkey wrote:I ordered the parts for the camlock breach today, had to go 3in, the 4in was going to cost $100 for the two parts, but designing around problems is why i do this.


Are you going to use a 3" camlock plug to close the rear or build out something different? This whole coax thing has me buzzing with some ideas...has been for some time actually but seeing a working unit here stoked it again for me. I don't expect them to be as efficient as a standard chamber/barrel design but there could still be some fun things possible.
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Unread postAuthor: Combustion Monkey » Tue Jan 13, 2009 5:26 pm

inonickname wrote:nice gun, not all new people come here displaying such ingenuity. Job well done


Thanks for the great compliment!

And to answer Starman
Starman wrote:Are you going to use a 3" camlock plug to close the rear or build out something different?


I had a set of camlocks kicking around for the barrel setup i mentioned so i scavenged them for the breach and here it is.

The new camlock breach on the Bettie

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When the new / longer internal barrel is built when i get the new cam set it will pass through the male cam fitting to nearly the back of the end cap.

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The new and old breach setup side by side for a comparison.

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The new cam setup will add 10in of overall length and the same amount of internal barrel. Once i get the new cams in i'll build the barrel and figure out how much volume i've gained by the water method. I shouldn't have to change my fuel meeter except for upping the pressure a tiny bit. I also may have just now come up with a way to stabilize the soon to be very long internal barrel, just have to make a run to the parts store tomorrow to see if it will work!

On a side note, I think that the necking down from 4in to 3in at the breach may cause a venturi effect and accelerate the force channeled into the breach area. Just a theory there, but I'd be interested to here any thoughts on that subject as well as any others.
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