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WIP Breech Loading Combustion

Post questions and info about combustion (flammable vapor) powered cannons here. This includes discussion about fuels, ratios, ignition systems, safety, and anything else relevant.
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WIP Breech Loading Combustion

Unread postAuthor: kjjohn » Tue Aug 17, 2010 8:57 pm

This is combustion cannon that I did a lot of work on earlier this year, but never got around to finishing. I will probably complete it once my birthday comes around, since I will be getting some extra money.

The chamber is 3"dia x 30"length DWV, but it's layered in couplings, so I figure it should be safe.

The barrel is 3 feet of 2" 6061-T6 aluminum, and I plan to polish it once the cannon is complete. The suppressor at the front was simply made with a 2"x3" bell reducer, and a length of 3" pipe, both painted black, and with several holes drilled in it. I'm not sure if it will have any effect, but it at least looks awesome.

The breech loader is an aluminum 2" camlock. The barrel slides back in its housing to allow breech loading.

I have installed the electronics box with the ignition system (the USG ignitor), but I haven't made the spark strip yet. I have also not made the fuel system, but it will be powered by MAPP, and utilize a 3-way ball valve for quicker metering.
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Unread postAuthor: Technician1002 » Tue Aug 17, 2010 9:17 pm

For a combustion a shorter larger diameter chamber is often better as there is less surface area for cooling for the same volume. Combustion completes faster in a short chamber for faster pressure rise.

Overall, I like it. The double layer is not needed as black ABS cellular core pipe has proven to work well in basic combustions.

Nice barrel. With the camlock this could be a very nice 1X hybrid.
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Unread postAuthor: kjjohn » Tue Aug 17, 2010 9:20 pm

Actually, it's not black ABS, it's just painted PVC. :D I wanted to go with a larger diameter chamber, but my local hardware store did not carry any kind of pipe over 3" that I felt safe using. Once it's complete, I may make some burst disks and try it as a 1x hybrid.
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Unread postAuthor: spudamine » Wed Aug 18, 2010 1:54 am

Thats looking really nice so far, I like the layering of the chamber, I've done it before in my PVC hybrid (see my sig) it gives a really solid feeling chamber, I had to dismantle it recently for space and out of interest I chopped the chamber in half, the solvent welds had taken perfectly and it looked like a single piece of tube with a 1/2" wall :D
From the picture it looks like your ali barrel is threaded, can you buy that or did you do it youself?
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Unread postAuthor: kjjohn » Wed Aug 18, 2010 11:46 am

From the picture it looks like your ali barrel is threaded, can you buy that or did you do it youself?


My uncle works at Wisconsin Metal Fab, so he got it threaded for me, however, you can get threaded Al pipe from McMaster as well. By the way, nice hybrid. I've never seen that one before.
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Unread postAuthor: Moonbogg » Wed Aug 18, 2010 8:10 pm

Why in the hell are people calling this a hybrid?
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Unread postAuthor: Gun Freak » Wed Aug 18, 2010 8:17 pm

I think it is because you could use a burst disk? I'm not sure, I always thought a hybrid was 2x and up and that all combustions are 1x.
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Unread postAuthor: jhalek90 » Wed Aug 18, 2010 8:40 pm

looks nice. as tech said, a smaller length chamber may improve performance.

Also, try using a 1-5 layers of aluminum foil on the cam lock, as a burst disk, just to help it build some pressure before it actually gets to the projectile.

it seems silly to use aluminum for the barrel, and settle for DWV for a chamber.... double layered or not, you best hope its not cellular core.

Im my opinion, DWV is retarded for use in any cannon.... its not like pressure rated pipe is that much more expensive... at least, not in the USA
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Unread postAuthor: kjjohn » Wed Aug 18, 2010 8:54 pm

The reason I didn't use DWV is not a cost issue. MY local store did not carry pressure rated pipe over 2". As for the aluminum barrel, I just had it laying around from another project that I could not complete due to cost, so I used it for the barrel.

In response to Moonbogg, it's obviously not a hybrid, I guess that term is kind of being thrown around loosely. What everyone is talking about is simply installing a burst disk in the coupling, or using it as a "1x hybrid".

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Unread postAuthor: bighead33 » Thu Aug 19, 2010 11:36 am

nice cannon but it's going to be hard to reload or put on a new burst disc with all those pipe clamps and all. you should probably update your design to accommodate a sliding mechanism for your barrel.
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Unread postAuthor: Gun Freak » Fri Aug 20, 2010 7:54 pm

@bighead, the barrel already slides, those are repair couplings. It is just like the old breech load on my golf ball cannon Superna! :D Great design for a breech load...
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