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Pneumatic Spud Gun Questions

Post questions and info about pneumatic (compressed gas) powered cannons here. This includes discussion about valves, pipe types, compressors, alternate gas setups, and anything else relevant.
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Pneumatic Spud Gun Questions

Unread postAuthor: zomgwtfbbq » Thu May 24, 2007 12:13 pm

Dear Spud people

I have a few questions that I cannot answer, perhaps you may help me answer them! The questions are written in the JPEG files! Thank you very much! :D

Yours sincerely

zomgwtfbbq
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spud2.JPG
spud3.JPG

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Unread postAuthor: mega_swordman » Thu May 24, 2007 12:33 pm

Question 1: You say significantly, so the answer is no. The U-bend will create a small amount of dead space; but depending on the length of the cannon I see, in which the elbows are right next to each other, there won't be enough power drop for it to be significant.

Question 2: The diagram is right, that is essentially how any breech loader works. the barrel may move back and forth, but it worth it for the convenience of the breech loader.

Question 3: yes the idea can work and does. See iknowmy3tables' Deus Ex Machina
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Unread postAuthor: Fnord » Thu May 24, 2007 12:39 pm

edit: wow you really beat me to this one mega.

#1 The u-bend may weaken it a little, but it probably wont be noticable. I think most u-bends you see in stores are dwv, though.

#2 since I didnt make the amr-1 and cant remember what it looks like I cant really answer this. You might want to PM the creator.

#3 It is possible, but batteries probably aren't the best choice if you want it to work. They are flat on the ends, which may cause jamming:
When a new round is pushed into the breech, the round below it will be pushed up against the round to be fired. When you attempt to close the breech, the pipe will be not be able to move back all the way because the next round will be catching on the edge of the pipe.

this problem may be solved by using rounded projectiles or by "knifing" the edge of the pipe.
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Unread postAuthor: zomgwtfbbq » Thu May 24, 2007 12:53 pm

Wow thank you very much for the instantaneous reply! Well done mega_swordman and _Fnord!

Oh and _Fnord, the battery was indeed an unforeseen problem, thank you for informing me!
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Unread postAuthor: Flying_Salt » Thu May 24, 2007 1:38 pm

Wait, I'm confused. Are you making an automatic loader to load and shoot batteries? If you're gonna be shooting batteries, it may not be worth it, because they fly horribly. You might want to try marbles, since you cannon seems to be a small bore.
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Unread postAuthor: zomgwtfbbq » Thu May 24, 2007 2:07 pm

Oh, I didn't know batteries would be bad projectiles. I was going for realism and just wanted something that would resemble a bullet and can be automatically loaded into the breech. But I guess since my barrel is not rifled, a spherical projectile is a better option.

Hmm... How am I going to make a realistic cartridge house marbles...

To the above posts: I realised an error that I have made. I meant magazine when I said cartridge.
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Last edited by zomgwtfbbq on Thu May 24, 2007 2:20 pm, edited 2 times in total.

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Unread postAuthor: mega_swordman » Thu May 24, 2007 2:09 pm

I think it was more for the theory, but I concur. i would instead use the method by iknowmy3tables: the cartridges in the Dues Ex Machina. That way, you can use a variety of objects as well as not encountering the problem _Fnord presented.
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Unread postAuthor: zomgwtfbbq » Thu May 24, 2007 2:19 pm

Yeah that is a great idea, except I do not really have a clue on how it works. I have just asked iknowmy3tables about his cartridge innovation by private messaging him, I hope he will explain it here in this thread later.
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Unread postAuthor: mega_swordman » Thu May 24, 2007 3:04 pm

I seem to full of answers today :D . Alright. from what I saw, he uses the same method as you described in diagram #3. However, instead of using the ammo by itself (such as the batteries) he uses small cartridges made of a coupler and bit of pipe. so the cartridge would be an extension of the pipe.

PS: I am sad to note that I made a good diagram in flash, but paint is a terrible program for converting over. I can give you the diagram, but you won't be able to read it. :sigh:
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Unread postAuthor: iknowmy3tables » Thu May 24, 2007 3:39 pm

now for the spud3 pic it should work with some adjustments, but first please avoid from saying automatic loader because auto and semi auto is actually short for "automatic loader" :lol: so the proper term is (magazine fed) bolt action
and just to let you know; my Deus ex Machina is fairly different in the way that it uses (how do I say this) real uhm forward locking bolt like in a real gun so my cartridge ejection system would work, you push the bolt forward then down to lock, unlike the AMR system (which is pretty common) where the barrel and bolt are the same and the action moves back and down to lock, its a good system because there is less dead space

you can do what flying salt is suggesting and use marbles because it's much easier to make bolts for sphere projectiles since you can make the magazine and receiver from pipe and pipe fittings

if you want batteries thats cool, being more original wont hurt, but there are some changes required. Like first the gap between the receiver wall and the opening of the barrel must be reduced or else the batteries or else the battery will just hit the side of the barrel

now I recommend this design if there is a pipe sleeve for a battery sized barrel for metric pipe I'm American and i've never used that so i don't know
Image
in this the design the light green pipe is the moving barrel and I recommend cutting a slot for the bolt with a router

however if the only sleeve you can get for the barrel is a sleeveable coupling then you'll have to try this where the front coupling is attached to the barrel/bolt
Image

remember if their is a lot of grinding down to make parts sleeve and you don't have a lathe, belt sander, or grinder (for metal) then you should ether find better sleeves or give up because it's way too flippin much work
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Unread postAuthor: iknowmy3tables » Thu May 24, 2007 3:56 pm

wow i took a lot of time to write that and slow down mega sword man the bolt is going the other way, and your forgetting the most important part, and thats the ejection mechanism it won't work in a sliding barrel bolt, if you know a way then I'd like to know for informational purposes

I'm planning on a how to for a lathe-less belt sander less version of my Deus ex Machina bolt. however it uses American pipe sizes
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Unread postAuthor: zomgwtfbbq » Fri May 25, 2007 1:01 am

Thank you for your time iknowmy3tables! I was pondering on how you made the ejection mechanism, that was ingenious! I am planning on making a realistic pneumatic spud gun that resembles an Accuracy International Arctic Warfare rifle.

Image

It would have a forward locking bolt action like yours and it would eject cartridges too. I was thinking of shrinking the cartridge to the size of a 7.62 × 51 mm NATO (around the size of an AA battery), and perhaps house a homemade nail dart.

Image

Could you perhaps explain on how you made your forward locking bolt action, cartridge, and magazine?

I know I am asking for a lot, but I am new to this and I appreciate you for your time. Thank you very much!
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Unread postAuthor: jackssmirkingrevenge » Fri May 25, 2007 1:09 am

here's an idea, if a tad complex: drill a couple of holes in the cartridges and you can have it eject them like a semi-auto, have a look here
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Unread postAuthor: iknowmy3tables » Fri May 25, 2007 6:10 pm

actually I thought of a similar blow back bolt that could do both, it was originally a design to reduce the the dead space and length in the bolt but it wasn't until I saw Jack's blow-back cartridge system that I realized it could be used as a select blow-back/bolt action so a lot of credit goes to Jack. I didn't use it in my deus ex machina because if I were to make it inline the dead space would not decrease dramatically. however it would if you used a piston valve or QEV it would have less dead space.
the system is just like my current deus ex machina only instead of a straight telescoping bolt it's a Tee one side of the bolt is capped and their are holes in the bolt for air to enter

I also would like to add that if you mainly want to shoot batteries and marbles then you could make a flexible non cartridge bolt action. if you really want to use other ammo then go with cartridges. and my cartridges can barley fit my nail darts so it probaly wont fit yours unless they are really short nails
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