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maximising FPS

A place to ask general spud cannon related questions.
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maximising FPS

Unread postAuthor: steelhead » Mon Sep 26, 2005 10:53 pm

I am going too build an all steel spudgun.
I want a coaxial design, and the dimentions are as follows:

reservoar data
Outer diameter : 4 inch
lenght : 20 inch
volume :215 in3

barrel data:
1,5 inc bore
lenght 45 inces

valve data:
4 inch diameter
seat diameter 1,5 inch
barrel seal type

according to GGDT v4.4 the muzzle velocity produced is around 306 fps if loaded with 20 PSI of air.

Any ideas/recomondations?

I do have acces to a metal spinning lathe...
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Unread postAuthor: drac » Tue Sep 27, 2005 5:39 am

If you use 100 PSI in a metal cannon, you could probably get close to supersonic, or past it. Definitely more than 100 PSI. Also, make the barrel about a foot longer, longer barrels always yeild more velocitty.
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Unread postAuthor: bubblebathman » Tue Sep 27, 2005 12:13 pm

yea but longer barrel u could have some down affects and great idea bout all steel i say go for it
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Unread postAuthor: boilingleadbath » Tue Sep 27, 2005 2:19 pm

What do you mean by "down affects"? I'll admit that a longer barrel is bulky, but a 4" steel cannon won't exactly be portable anyway.

Anyway, what is the projectile mass here? I'd venture to geuss about 15-20 grams.
(and how long is the barrel?)

You might want to make the barrel bigger, possibly 2".

I often don't understand the reasons of people making metal cannons - they build said cannon, but then they only pressurize it to 100-150 psi. I mean, what's up with that?! Normal sch 40 is rated to 3-2 times that, and even sch 80 is cheaper than steel. I mean, what's the point of making a cannon out of material that can safely take 800 psi, and then pressurizing it to 100?
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Unread postAuthor: laz91 » Wed Sep 28, 2005 3:54 pm

what at 20 psi 320 fps that doesn't sound right at all how can it go that fast with so little psi?
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Unread postAuthor: drac » Wed Sep 28, 2005 3:59 pm

Because the flow on a piston valve is so high, it pushes it out harder and faster (oh god, that sounded wrong :oops: ). People can vaporize spuds with a properly made piston gun.
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Unread postAuthor: boilingleadbath » Wed Sep 28, 2005 4:56 pm

The ammo is light weight - that's the only possibility:
I made a rough model of this gun using the GGDT, but used a burst disk with 80% flow instead of a piston valve (G#1). A second model was made, using a 3 oz piston and a .5" vent, 50% flow (G#2).

G#1 reached 304 feet/sec at 20 psi with a 23 gram projectile.
G#2 reached 307 feet/sec at 20 psi with a 21 gram projectile.

(I said 15-20 gram, didn't I?)
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Re: maximising FPS

Unread postAuthor: frankrede » Wed Aug 30, 2006 6:25 am

steelhead wrote:I am going too build an all steel spudgun.
I want a coaxial design, and the dimentions are as follows:

reservoar data
Outer diameter : 4 inch
lenght : 20 inch
volume :215 in3

barrel data:
1,5 inc bore
lenght 45 inces

valve data:
4 inch diameter
seat diameter 1,5 inch
barrel seal type

according to GGDT v4.4 the muzzle velocity produced is around 306 fps if loaded with 20 PSI of air.

Any ideas/recomondations?

I do have acces to a metal spinning lathe...

AT 20 psi?Wow,in my pneumatic at 20 psi. The potato would roll out of my barrel.Jk,I havent tryed it at 20, It works fine at 130
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