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Built a pneumatic 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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Unread postAuthor: bboymatty » Tue Apr 24, 2007 9:29 pm

As to everyone who is saying the chamber is too small, in terms of looks maybe it is, but it is certainly not in terms of performance. Remember that the barrel is about 13.5mm diameter, and only a meter long, while my chamber (if it was stretched out) would be 40cm long and 32mm diameter. Add the lightweight of the darts and you see that the chamber produces far more propulsion than what is needed.

Yeah Hotwired the pipe walls are exceptionally thin, maybe 3/4 of a mm. I seriously use any type of AA battery i want. Ill post some pics into my entry.

Wannabe ill have some damage pics up soon mate.

VH_man, i put a little dab of hot glue down the dart when i have assembled each one. It stops the nail from falling out during firing. So far its worked perfectly and one hot glue stick gives enough for about 100+ rounds. So its cheap too!

The barrel is quite easy to understand, harder to make. I start with a length of 25mm pipe, two 20mm couplings, 1m of 20mm pipe, and 1m of 15mm stainless steel. the couplings are sanded out to allow the 20mm to slide completely through snuggly, and then are glued into place inside the 25mm pipe. then i used some expoxy and glued the stainless steel barrel inside the 20mm PVC tube. Its a little fragile so you have to be careful.

Then i got my dremel and cut out a breech on the 25mm, and then somehow inserted the 20mm PVC into its couplers and glued on a little handle, through the breech hole. difficult. once that was done i bought a 25mm to 20mm bushing, cut it right down so it would fit inside a adapter with enough room for the 25mm pipe to be glued in too. then i just attached it to the solenoid and painted it!

I have added a new picture to my entry to kinda show you the inside of the pipe.

Shadowscion, i have a bushing inside that the barrel is placed into when you lock the breech. It isnt sealed with a o ring or anything, because when you lock it in it goes in very tight, and doesnt come out during firing. No air is leaked around the barrel either.
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Unread postAuthor: iknowmy3tables » Wed Apr 25, 2007 7:27 am

well I geuss its nt that small for your barell size, but the gun still is not a as strong as most rifles on the forum
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Unread postAuthor: chaos » Wed Apr 25, 2007 6:45 pm

do you know the grade of stainless the barrel is made from? i would imagine its not that strong if you got it from bunnings still its more than sufficeiant for this gun.
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Unread postAuthor: bboymatty » Wed Apr 25, 2007 10:48 pm

I guess power is a matter of opinion, for my needs this gun is much more than enough, but i guess if you wanna go firing 4" long lead slugs then you might need something else.

and yeah no idea on the grade. Personally im not fussed because i have dropped cannons before and they have snapped in two, so im very careful about how i treat this little guy. Its more than enough for the gun.
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Unread postAuthor: joe blogs » Fri Apr 27, 2007 4:24 am

I am questioning if i have any hope of winning the competition thanks to your gun.
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Unread postAuthor: Hotwired » Fri Apr 27, 2007 4:34 am

joe blogs wrote:I am questioning if i have any hope of winning the competition thanks to your gun.

Your chances increase enourmously by actually entering a cannon :wink:
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Unread postAuthor: bboymatty » Sat Apr 28, 2007 5:39 am

hahaha what hotwired said, come on man get it in quick smart!

its not about winning really, its about getting some incentive for innovation and originality among the community :)
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Unread postAuthor: XxtriviumxX » Mon Apr 30, 2007 4:10 am

that gun is a piece of work, very nice :D i really like the chamber/stock idea :D
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Unread postAuthor: mega_swordman » Tue May 01, 2007 5:13 am

I apologize if this is an extremely simple question, but how do you make the gun more accurate? Is there any way to make it more accurate besides extending the barrel? I just felt that this would be a good area to ask.
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Unread postAuthor: integral » Tue May 01, 2007 5:21 am

The type of ammo you are shooting greatly determines how accurate the cannon will be. Spherical rounds such as marbles and sinkers offer greater flight stability in smoothbore situations. Cylinderical (sp?) rounds tend to "tumble" when fired diminishing your effective range/accuracy. To overcome this the cylinderical round must be stablized (sp?) by either balancing its weight (towards the front) or using fins/tails.

Another factor in accuracy is how tightly the round sits in the barrel. If the round requires some wadding, then the trajectory will vary, where as snuggly fitted rounds offer more consistent results. The other obvious solution would be using a rifled barrel but often these are too tedious to make.
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Unread postAuthor: bboymatty » Tue May 01, 2007 10:57 am

what integral said is completely right, but i would also add that in some instances the amount of pressure your putting behind the projectile can have a positive or negative impact on accuracy, for a number of reasons including velocity (being less prone to windage) and bullet drop.

Ive found sometimes if i overpressurise i can destroy the round before it even gets out the barrel, but this only really is applicable if your using vegtables like potatoes and carrots. (mine used to blow up in a fine spray haha)

For my accuracy, i use a long barrel (for max velocity), a snuggly fitting (in the barrel) round (prevent ricochet and stabilise flight trajectory) a fin-stabilised round (light, open-ended dart which 'wants' to fly through the air, nail first), high pressure and of course zeroed in iron sights or scope.

hope it helps :)
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Unread postAuthor: chaos » Tue May 01, 2007 4:35 pm

have you tied those tinie winie marbles you can get they like 12mm?? ive got 2 of them and they are no use to me.

also can you please try some lead fishing sinkers, im sure you could use a lot of pressure with them.

im sure with both of these you should get good results.
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Unread postAuthor: bboymatty » Wed May 02, 2007 10:17 am

yeah i want some of those marbles. i found 1, used a bit of wadding and shot it at a tree and the bloody thing splintered like a [female doggy] really well. I dunno where to get them from!

any help?
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Unread postAuthor: integral » Thu May 03, 2007 2:05 am

Wollies? I'm pretty sure I saw a bag there for like 4AUD (I think it was a pack of 20 marbles). I also saw a bag of 6 big heavy glass marbles for 5.99AUD that looks like it would fit a 25mm barrel.
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Unread postAuthor: VH_man » Thu May 03, 2007 9:13 pm

my local craft store sells bulk packs of marbles... my parents wont let me shoot them though...... kinda annoying. oh well, darts are more fun....................
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