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full sized GB hybrid

Post questions and info about hybrid (compressed gas with fuel) powered cannons here. This includes discussion about fuels, ratios, ignition systems, build types, safety, and anything else relevant.
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full sized GB hybrid

Unread postAuthor: SpudFarm » Tue Mar 11, 2008 2:42 pm

i am looking into making my next cannon. i have totally stopped making combustions and pneumatics so from now on it is hybrids.

some basic questions.

1. i am going to use 3" or 4" steel chamber how high can i go with that.
2. the chamber is going to be about 12" is there any risk of DDT at 5x?
3. the barrel is going to be 1.5" stainless, how long?
4. is it safe to ask a welder to weld thick steelplates to the ends of the chamber then make holes and weld in fittings?
5. do ordinary steel fittings become brittle under welding?
6. what do you think?

this time it is probably going to be made. i got $310 at this point and i am going to sell my pneumatic for $240 and i have some archery behind me and got a compound bow i am going to sell for $600. (mabe i sell my hybrid for $400 if needed)
so in a while i got $1150 ($1550) and i think i can get the materials for that.

do you think it is worth to sell my guns to get one freaking awsome gun?
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Last edited by SpudFarm on Sat Mar 15, 2008 8:33 am, edited 1 time in total.
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Unread postAuthor: DYI » Tue Mar 11, 2008 3:09 pm

1. If it is SCH 40, 10x would still leave you with a safety factor of ~2, and I don't think it would be handheld, so 10x sounds like a reasonable limit. You could go higher (up to maybe 15x or so) if you weren't anywhere near it when it went off, and didn't value it too much.

2. Not with any conventional fuel/oxidiser mix, or even oxy/propane. Remember that DDT runup distance is directly related to the diameter of the vessel it occurs in. A 4" pipe should have ~2x the runup distance of a 2" pipe (this is a good thing, it makes DDT less likely in larger diameter pipes).

3. With a 150 ci chamber (4" x 12") and a 10x mix, the 1.5" barrel should be about 76 feet long - so make it as long as you can.

4. If that welder is good enough to weld on high pressure vessels safely. If he isn't certified to weld on pressure vessels, it would be a good idea to test the welds with pressurised water first, at the intended operating pressure.

5. Ordinary steel fittings will be fine. On a side note, where do you plan on getting steel fittings? I've never seen anything but malleable iron fittings at my hardware store, and there are no steel fittings on any of your launchers either.

6. I think that it sounds uncannily similar to the hybrid in my sig, which I now only need fuel metering and ignition for, all of which will be arriving in early April.

7. I think that, considering the hybrid in my sig (which is identical in nearly every way to yours) will cost me less than $300 in total, you don't need to give up any of your possesions to build it. If you can find a friendly welder, the materials and welding could be accomplished for under $50 (mine was $30, but I got the pipe and plates free from my school).
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Unread postAuthor: SpudFarm » Tue Mar 11, 2008 4:30 pm

that was to big help :)
the welder says he is licenced but i want to look at the licence before letting him loose.

i am going to the pipe shot and hear if they got all the pipes and fittings and get a price. then i will keep you updated.

and would a aluminium cam lock be safe and do you think it will seal with the burst disk?
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Re: full sized GB hybrid

Unread postAuthor: STHORNE » Tue Mar 11, 2008 4:34 pm

spudfarm wrote:do you think it is worth to sell my guns to get one freaking awsome gun?


Hellz to the Yeah!!! then instead of a bunch of average guns, you would have one kick ass one that not a lot of other people have. Well, whatever you decide to do, good luck!
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Unread postAuthor: DYI » Tue Mar 11, 2008 5:01 pm

An aluminum cam lock may not be very safe at 10x mixes - they're only rated for 250 psi in most cases. If you really want ease of use, you could always machine something similar yourself. Take a look a Dumbaascii's Taternator II for the disk holder side of things. If you can't afford machining, I'd just advise a union. That's what I'm doing.
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Unread postAuthor: STHORNE » Tue Mar 11, 2008 5:07 pm

DYI wrote:An aluminum cam lock may not be very safe at 10x mixes


spudfarm wrote:the chamber is going to be about 12" is there any risk of DDT at 5x


I don't think spudfarm plans on taking it past 5x, but i might be mistaken.
Spudfarm? What's you're take on this?
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Unread postAuthor: SpudFarm » Tue Mar 11, 2008 5:14 pm

i am using it at 5x at most but some 6x now and then probably.
if i try i can probably get a stainless but do you think the alu cam lock would be safe at 6x?
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Unread postAuthor: STHORNE » Tue Mar 11, 2008 5:21 pm

aluminum cam lock @ 6x = relatively unsafe

EDIT: Oops, typo, my bad
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Unread postAuthor: bigbob12345 » Tue Mar 11, 2008 5:24 pm

Im going to have to strongly disagree there sthrone.
a 6x mix would produce pressures more than twice its rated pressure.
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Unread postAuthor: DYI » Tue Mar 11, 2008 5:27 pm

6x = ~700 psi
alu. cam lock rating = 250 psi

Decide for yourself. I use parts at more than 3 times their rated pressure on the SCTBDC, so I'm really not the one to talk.
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Unread postAuthor: SpudFarm » Tue Mar 11, 2008 5:27 pm

so then i get a steel one...
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Unread postAuthor: STHORNE » Tue Mar 11, 2008 5:31 pm

steel would be the best way to go if you wanted to stay within the "safe-zone". Unless you wanted to stay in the 2-3x region, steel would be your best bet.
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Unread postAuthor: bigbob12345 » Tue Mar 11, 2008 5:35 pm

just had a look on mcmaster and the steel ones are rated no higher than the aluminum ones so I recommend you just use a union.
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Unread postAuthor: SpudFarm » Tue Mar 11, 2008 5:40 pm

nooooooooo!!!!!!!! i hate cutting burst diks :O
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Unread postAuthor: Fnord » Tue Mar 11, 2008 6:12 pm

nooooooooo!!!!!!!! i hate cutting burst diks :O


Wouldn't you have to cut burst disks for pretty much anything you use? Or is my lack of understanding of cam-locks misleading me?
You could always weld up a piston valve that'll tear itself apart after 3-5 shots :P

I use parts at more than 3 times their rated pressure on the SCTBDC, so I'm really not the one to talk.


Um, you use unrated abs at 500 psi :lol:
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