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GGDT -Proje never cleared muzzle but actually went 40 yards

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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GGDT -Proje never cleared muzzle but actually went 40 yards

Unread postAuthor: BCannon » Thu May 10, 2007 12:50 am

GGDT shows my Projectile never cleared muzzle but it actually went 40 yards. I know I'm just entering something wrong. Does anyone know what it is? I have attached a capture of GGDT.

My gun consists of:

Chamber is 4" sch 40 by 12 " long, pressured to 80 psi => inline 1" sprinkler valve actuated by a momentary switch => Barrel is 4" sch 40 by 16" long => projectile is 3" wide by 10" long, 1 pound, with a rag stuffed in the barrel for a packing wad.
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Attachments
GGDT error.jpg
GGDT Capture

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Unread postAuthor: MrCrowley » Thu May 10, 2007 1:44 am

Why do you have a 4" barrel with a 4" chamber? :P You've got more volume in the barrel then chamber and with such a large bore im not suprised it only went 40yards,infact i am suprsied it went 40yards. Its because of the wadding that it went that far without it the projectile wouldn't clear the barrel.
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Unread postAuthor: clide » Thu May 10, 2007 1:53 am

Your dwell time is set to 0 which means the valve closes immediately after opening. Set it to something high like 1000.
You probably shouldn't be using generic anyway since GGDT has settings to model pilot valves.
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Unread postAuthor: jackssmirkingrevenge » Thu May 10, 2007 2:16 am

your dwell time's 0 :?

edit: hadn't seen clide's post :oops:
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Unread postAuthor: frankrede » Thu May 10, 2007 6:48 am

I fiund it hard to believe that your cannon made that distance.
I have one with a similiar setup except I have a 3" barrel.
Adn even with a pefect airtight sabot I could barrely get 10 ft
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Unread postAuthor: BCannon » Thu May 10, 2007 8:56 am

Thanks! That was the problem.

Clyde, I don't see an option for pilot valves. I have the following options: Chamber Seal, Barrel Seal, Burst Disc, Hammer and Generic in version 4.4. What version are you using?

frankrede, the projectile goes 40 yards with a t-shirt stuffed tightly in the bottom. GGDT shows a greater distance but I'm probably not holding the gun at a 45 degrees angle.
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Unread postAuthor: clide » Thu May 10, 2007 1:56 pm

Chamber and barrel seal are different configurations of pilot valves. Most sprinkler valves are barrel seal.
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Unread postAuthor: super spuder » Thu May 10, 2007 3:33 pm

sorry, but could someone send me a link on where to download GDT.
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trying to decide on a new project, probably something small.
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Unread postAuthor: pyromaniac » Thu May 10, 2007 3:45 pm

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Unread postAuthor: BCannon » Thu May 10, 2007 4:01 pm

Oh, I thought that was referring to only a barrel sealing piston valve. So, if I'm using an unmodified 1" Orbit WaterMaster sprinkler valve, how should I adjust the following settings?

- Piston Dia
- Piston Mass
- Vent Dia
- Pilot Vol
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Unread postAuthor: BCannon » Thu May 10, 2007 7:35 pm

I found it with a search:

Valve type: Barrel sealing
Piston seat diameter: 1.2"
Piston diameter: 2"
Piston mass: .8oz
Flow efficiency: 23%
Pilot volume: 1.1 in3
Dead volume: 2.2 in3
Vent Diameter: .1" (.2" if you modded your blowgun)

The guy that wrote this is a genius! GGDT says my projectile will go 41.33 yards and it went 40 yards according to my range finder.
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