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Building a Marble/Cork Gun

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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Building a Marble/Cork Gun

Unread postAuthor: ammosmoke » Thu Jun 26, 2008 6:29 pm

Ok, so as the title says, I will be building an over-under gun of about marble caliber. So far what I've got is a 1/8" qev shuttle for actuation, a blowgun to actuate that, and a 14" 1 1/2" steel chamber that I was going to use for my airsoft project, but gave up because I decided it was too boring/not worth it. I am planning on having a removable threaded copper barrel, and a piston valve. I will probably have a removable silencer on the thing, because of the area I live in. Making a silencer could be a bit of a challenge, but that's ok. There is plenty of pages around here to help me with that part. So, does anybody have some suggestions as far as overall design? Anything in particular you like to use for pistons? I'm at a loss for choosing a material as of now. I've already got tire tube for a sealing face though. So, start posting!
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Unread postAuthor: POLAND_SPUD » Thu Jun 26, 2008 7:32 pm

first of all you can use a 3/4" QEV to make it look neat and easier to build....

there are several possible designs here. The fact taht you are going to use a qev for piloting gives you a lot of freedom. I think that you can try to build it like hotwired build his gun as it gives you the longest lenght of barrel when compared to overal lenght.... if you are interested I can add basic drawings

EDIT ok pic added the last one would resemble a real gun and offers good performance...
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Unread postAuthor: ammosmoke » Thu Jun 26, 2008 11:32 pm

Thanks Poland Spud for the ideas, that was exactly what I was looking for. Maybe I should have been a little more clear in the beginning, but I was looking for some over-under configuration suggestions. Since I'm looking to make this relatively quickly, (going on vacation at a lake) I may put in a metal ball valve as a temporary substitute for a piston.
Anybody else want to add something?
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Unread postAuthor: POLAND_SPUD » Fri Jun 27, 2008 2:51 am

well that changes everything...if you want to use a BV you will need completelly different designs... the good thing is that you can convert it to proper QEV/piston valve gun afterwards if you use malleable iron threaded fittings....

the most basic and comfortable design would consist of (starting from the muzzle): BARREL - 16mm/ X" compression fittng - BALLVALVE - nipple - T with an endcap on one end and joining with a chamber bellow...

choosing the size of fittings is up to you - but if you want to maximize performance stick with 3/4" for 16mm barrel

please give more specs - what lenght of barrel what size of chamber etc.
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Unread postAuthor: ammosmoke » Mon Jul 07, 2008 1:15 am

Ok, I know this is a while later, but... Now that the pressure is off for getting it done quickly, I am going for the piston. I already said the chamber size (1 1/2 by 14"). The barrel is going to be interchangeable between 1/2" and 3/4". So, I will probably have a 1" piston housing and adapt it down to 3/4" threads for the barrels. And the same for the silencer. I think that my barrel is going to be in the 3ft range. GGDT says it should be in the 260fps range at 120psi. That seems a little low to me... And it doesn't seem to want to calculate properly when I tell it my actual inner diameter. When I do that, it says that my chamber volume is 3in^3. What is up with that? If I place the inner diameter as 0, it says 24in^3 or so, which sounds about right, because if my chamber were a square prizm, it would have 31.5 cubic inches of space. I'll attach it to see if you guys can find the problem. Maybe it is something really obvious that I'm not getting.
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Unread postAuthor: POLAND_SPUD » Mon Jul 07, 2008 2:37 am

oh dude... it's quite easy.. this function of GGDT is for coaxials... so if you have a normal gun (not a coaxial) you put '0' (zero) for chamber ID.
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Unread postAuthor: ammosmoke » Mon Jul 07, 2008 1:40 pm

Ohhhhh that is why! Thanks. :oops:
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Unread postAuthor: nickz » Tue Jul 08, 2008 5:28 am

I just built a very similar gun, mine has a 1 1/2 x 2 foot Sch 40 Pvc chamber

and a 1/2 x 3 foot Sch 40 pvc barrel. I am using a ball valve to shoot it though. I am also going to put a 5 foot barrel on it soon.
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