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my gun

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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my gun

Unread postAuthor: McFear » Sun Feb 03, 2008 7:21 am

Hey,

I just joined SpudFiles.com and would like to share my story.

I just made an AWESOME gun. fairly bulky though.

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As can be seen in the photo, its big. the two chambers are 100mm diameter pvc and 400mm long.The barrel is 65mm diameter and 2m long. This does not meet with the 1 : 1.5 ratio and is more like 1 : 1 but it still shoots hell far.

i am using aerostart spray as a fuel and as an ignition source i am using a bbq ignitor.

when i first shot this thing, i had a tennis ball rammed down the barrel which is also the only thing i shoot with it. i rammed the ball down the barrel, put a 3 second burst of aerostart in each barrel and put the end caps on. aimed up the hill in the general direction of my house and pushed the button. The gun blew back about a foot from recoil, and the ball flew straight at the house, upon impact with the veranda the entire ball exploded and i still have yet to find the remaining quarter of it. some parts of the ball are imprinted into the wood and wont come out. this is mainly fur though. The balls also cant be used after about 5 - 10 shots because the fur is melted off them and they dont seal anymore.

i have also just made a pnuematic cannon with the same specs. The only difference is that it has a tubeless tire valve in the end and a ball valve just before the barrel. i charged it up to 35 psi and when i was holding it when charging it blew the cap that was supposedly meant to be glued on off while i was holding it. IT HURT LIKE HELL. i hadnt let the pvc glue dry properly. after fixing the end and replacing the tire valve cause the original shattered on impact with the shed wall, i let the new end and valve dry for 24 hours and then charged to 30 psi. so i wouldnt lose the tennis ball i put a bucket on the end of the barrel.

in short. no tennis ball. its gone. and also no bucket. there is no floor in it.

will hopefully put some videos on the net of the cannons firing. the combustion cannon shoots a tennis ball about 400 - 600+ m. my property is 10 acres and from one end of the property, shooting uphill we lost the ball. thats about 400m + so i have no real idea about the range of the gun.

if needed i can post blueprints of the cannons as i have made them to anyone in the world. but a small fee for postage will occur.

thanks.

McFear
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Unread postAuthor: Novacastrian » Sun Feb 03, 2008 7:45 am

:D :D :) :) :( :( :o :o :shock: :shock: :? :? 8) 8) :lol: :lol: :cry: :cry: :oops: :oops: :P :P :x :x :evil: :evil: :twisted: :twisted: :roll: :roll: :wink: There is no fee for that.

Well, come to spudfiles.
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Unread postAuthor: schmanman » Sun Feb 03, 2008 8:18 am

novacastrian, you are too bland.


you need to use more smilies. :wink:

some nice mid-sized cannons you've got there, although a bulk of the parts on the pneumatic are not pressure rated.
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Re: my gun

Unread postAuthor: Ragnarok » Sun Feb 03, 2008 8:38 am

McFear wrote:the combustion cannon shoots a tennis ball about 400 - 600+ m. my property is 10 acres and from one end of the property, shooting uphill we lost the ball. thats about 400m + so i have no real idea about the range of the gun.

I have to express my doubt at these figures. Those sound far too high for the type of cannon you're using.

We do get a lot of people through with far more extravagant range figures though. The truth is, guessing ranges is very hard unless you've got a lot of practise, and usually, I'd say that guesses are normally twice as generous as they're likely to be firing - mostly because a small object travelling that fast at those distances naturally appears further away than it really is to the untrained eye.

Welcome to the site though.
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Re: my gun

Unread postAuthor: Carlman » Sun Feb 03, 2008 9:13 am

McFear wrote:if needed i can post blueprints of the cannons as i have made them to anyone in the world. but a small fee for postage will occur.

thanks.

McFear


hehe, you want to sell them lol

im sure i could salvage the pvc that you used for a barrel for something :D

sorry that just made me laugh

um yea...welcome
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Unread postAuthor: LikimysCrotchus5 » Sun Feb 03, 2008 9:22 am

Those are pretty nice cannons for a start i would say but the ranges, just as ragnarok said are most likely incorrect and it would be better if you actually measured the distance so you know for sure.

I dont think we will be needing any plans for these cannons because we have far more advanced cannons on this site, only to speak the truth and not offend you.

But its great for a start. If you pursue this hobby, you will find out how to make cannons more powerful and effiecient.

Although i would say that the pneumatic is somewhat efficient because of the long barrel it has for a ball valve.

Welcome to spudfiles :)
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Unread postAuthor: DYI » Sun Feb 03, 2008 9:37 am

Although i would say that the pneumatic is somewhat efficient because of the long barrel it has for a ball valve.


The combustion is reasonably efficient. If his specs are accurate, the C:B ratio is ~0.95:1. This means that the barrel is about 1/5 the length it should be to be efficient. That isn't anywhere near reasonably efficient.

And to the OP, we don't ask for plans here, and we don't use 'em. If you can't figure out how to build something by looking at it, you probably shouldn't be building it in the first place.
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Unread postAuthor: frogy » Sun Feb 03, 2008 12:26 pm

DYI wrote:
Although i would say that the pneumatic is somewhat efficient because of the long barrel it has for a ball valve.


The combustion is reasonably efficient. If his specs are accurate, the C:B ratio is ~0.95:1. This means that the barrel is about 1/5 the length it should be to be efficient. That isn't anywhere near reasonably efficient.


How is the barrel 1/5 the length it should be if the ratio is .95:1...

Unless I'm doing something wrong...
100mm / 2 = 50^2 * pi * 400mm = 3141592.65 x 2 = 6283185.30
65mm / 2 = 32.5^2 * pi * 2000mm = 6636614.48

0.9467 - C:B

Where optimal C:B ranges from .6 to 1.5 for combustions... I like .8 myself, his barrel should be 4188790.2 cubic mms... Which would make his barrel 1262 mms... 1.5x too long
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Unread postAuthor: Ragnarok » Sun Feb 03, 2008 12:33 pm

@frogy: DYI was talking about the pneumatic's barrel being too short, not the combustion's.
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Re: my gun

Unread postAuthor: jimmy101 » Sun Feb 03, 2008 1:05 pm

Welcome to the forum.

Nice first guns. As you've discovered, spudguns ain't toys ...

McFear wrote: the combustion cannon shoots a tennis ball about 400 - 600+ m. my property is 10 acres and from one end of the property, shooting uphill we lost the ball. thats about 400m + so i have no real idea about the range of the gun.

I suspect your distance figures are a bit off. An acre is a square chunk of land that is ~210 feet on a side. A square ten acre lot has an edge length of sqrt(10)*210ft=664ft=221yards=202meters.

The diagonal of a square, 10 acre lot is ~312 yards (285 m).

You might want to pace off your range, figure your stride is 3 feet (0.9 m). Or, use Google Earth.
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Unread postAuthor: jimmy101 » Sun Feb 03, 2008 1:19 pm

Ragnarok wrote:@frogy: DYI was talking about the pneumatic's barrel being too short, not the combustion's.

Uh, no. DYI said;
DYI wrote:The combustion is reasonably efficient. If his specs are accurate, the C:B ratio is ~0.95:1. This means that the barrel is about 1/5 the length it should be to be efficient. That isn't anywhere near reasonably efficient.

Not exactly sure what DYI was trying to say. I think the "1/5" is a typo and DYI meant "1.5". The gun should be "reasonably efficient", given that "efficiency" and "combustion spudgun" really don't belong together. :D
Not sure why DYI says "The combustion is reasonably efficient" and then says "That isn't anywhere near reasonably efficient". Is he switching between the combustion and pneumatic designs?

Looks to me like the combustion's design is OK. Not perfect, but a good first gun.

The double chambers really doesn't accomplish much except keeping the length of the chamber small. Since McFear will obviously want to add a chamber fan to his next gun, the double chambers are kind of a PITA since they'll each need a fan.

Plus, given the recoil energy of a gun this size, there is a heck of a load on the fittings between the two chambers. Put a couple t-balls in the barrel, push the breech end of the gun up against an immovable object, and the gun will probably destroy itself when fired.
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Unread postAuthor: LikimysCrotchus5 » Sun Feb 03, 2008 1:26 pm

Yea i was confused as well but i just didnt bother. He wasnt using specific subjects so i really couldnt understand if he was contradicting himself in 2 sentences.
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Re: my gun

Unread postAuthor: MrCrowley » Sun Feb 03, 2008 1:27 pm

McFear wrote:it blew the cap that was supposedly meant to be glued on off while i was holding it. i hadnt let the pvc glue dry properly.

As far as I can see your pneumatic cannon has a fair amount of DWV. Hence the cap blowing out. DWV isn't pressure rated.

Also you really need to wait the 24hours, if you can't wait 24hours, build a cannon out of metal and threaded fittings. Otherwise you have to wait the specified time, it's not worth the risk, which you know all too much about now.

McFear wrote:if needed i can post blueprints of the cannons as i have made them to anyone in the world. but a small fee for postage will occur.


No, I think we're all right with the blue prints :wink:
Don't want to teach people that it's alright to use DWV :)

Other than that, nice combustion, but you ain't getting 400-600m :)
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Unread postAuthor: Ragnarok » Sun Feb 03, 2008 1:47 pm

@jimmy101: It is put like that, but you have to take it in context with the quote that was actually in the post.

DYI knows his facts, and I'm certain he was talking about getting to the "ideal" 0.2:1 ratio, which you would get if you made the barrel of a 0.95:1 launcher 5 times longer - well, you'd get 0.19:1.

I read it as:
The combustion is as close to being as efficient as it can be.
(He then switches back to talking about the quoted post, so talking about pneumatics again) ...If his specs are accurate, the C:B ratio is ~0.95:1. This means that the barrel is about 1/5 the length it should be to be efficient. [That ratio] isn't anywhere near reasonably efficient [for a pneumatic].


I think that's what he meant there.
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Unread postAuthor: jimmy101 » Sun Feb 03, 2008 3:02 pm

Ragnarok, ya, I think you're write, my brain just couldn't parse the post. DYI has more of a pneumatic point of view, mine is more combustion.

Of course, actually making a pneumatic gun to a CB of 0.2 is pretty silly, you'll get much better performance with a bigger chamber, it just won't be as efficient.

If you are pumping the chamber up with a bike pump the efficiency is relavant, if you are using a compressor then it is pretty irrelevant.
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