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Flipping the script: take a cue from Spigot/Rifle grenade?

A place to ask general spud cannon related questions.
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Flipping the script: take a cue from Spigot/Rifle grenade?

Unread postAuthor: TapTheForwardAssist » Tue Dec 16, 2008 5:52 pm

Greetings, I'm not experienced in the spud-cannon scene, but used to be a professional artilleryman (11th Marine Regiment), and always though the idea of spud-cannons to be pretty awesome.

I've been messing around a bit with rifle-grenades (inert) launched off my AR-15. Then I did a bit of reading about spigot mortars, and I suddenly wondered if similar concepts have much traction in the spudgun community.

Basically: rather than have a tube with a projectile that fits in the bore, does anyone build a tube around which the projectile fits?

For example, a rifle grenade, which is launched by a bullet or blank cartridge fired from a rifle: http://www.youtube.com/watch?v=QGVs4fynFxk

Image

A spigot mortar is, externally, somewhat similar, with the big difference being that the launching charge is generally in the mortar round rather than in the tube:

Image


Would there be any advantage to messing with this design from a spudgunner perspective? Upsides would include being able to make projectiles in a wide variety of shapes, unencumbered by the constraints of the bore. Further, you can stabilize via fin rather than by rifling, avoiding the inherent hook/slice of a spinning projectile.

You could also launch a relatively wide projectile from a very slim high-pressure tube.

Is there any merit to the idea, has it been done before, or is it just markedly inferior to conventional spudsmithing?
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Unread postAuthor: SEAKING9006 » Tue Dec 16, 2008 5:57 pm

Well, nobody's really tried it. Most pneumatics operate on the principle of 'make the barrel longer!' where we really haven't put any thought into short-barreled guns. But were always excited by new and unique cannons. Build one, and see how it does.
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Unread postAuthor: Sticky_Tape » Tue Dec 16, 2008 6:01 pm

I think that some people did that with cardboard tubes that fit over their barrels. It's a great idea but one you have to make it instead of buy a bag and two you would have to make it light and long for decent volocity.
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You can tell how awesome a cannon is by the pressure used.
http://www.spudfiles.com/forums/high-pr ... 12803.html
xnt rnm ne z ahtbg
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Re: Flipping the script: take a cue from Spigot/Rifle grenad

Unread postAuthor: judgment_arms » Tue Dec 16, 2008 6:06 pm

I've toyed with it, but since 90% of what I do is paintball related I never put to much work into it.

I did throw a half inch barrel on one of my cannon and took two, two litter bottles duct-taped together back to back and filled with water one caped the other slid over the barrel (think water rocket).


didn't do much, but sure as heck looked cool! :D


TapTheForwardAssist wrote:... spudsmithing?

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Unread postAuthor: FishBoy » Tue Dec 16, 2008 6:07 pm

I made a 3' long (inert) missle which slid over a 3/4" barrel & got some amazing range with it.

edit- link- http://www.spudfiles.com/forums/3-4-car ... 15425.html

(this was it in it's most basic form)
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Unread postAuthor: TapTheForwardAssist » Tue Dec 16, 2008 6:24 pm

FishBoy wrote:I made a 3' long (inert) missle which slid over a 3/4" barrel & got some amazing range with it.

edit- link- http://www.spudfiles.com/forums/3-4-car ... 15425.html

(this was it in it's most basic form)


Amazing range? How amazing are we talking here? Now I'm curious!


That toy thing in the link claims to get 1000ft straight-vertical, and those are some tiny 3/4" rockets, and using a really inefficient-sounding gasket-failure trigger system. I'd imagine one could do a lot better with some proper smithing, a 45deg angle, even using the same $2 foam rockets you can buy from that company.

@FishBoy: Your pic is pretty much exactly what I was envisioning. Do you have any longer write-ups, or did you end up giving up on the project?

I won't have time to try and build until January at the earliest (and am also busy writing a thesis and rebuilding a Honda PA50 moped), but would such a creature be pretty easy to build for a novice? It seems to be a pretty standard build, just with a thin/short barrel compared to most. Is it difficult to get sufficient pressure and release it quickly enough to get a good launch?
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Unread postAuthor: SP00K » Tue Dec 16, 2008 6:31 pm

O! I made a miniature "grenade launcher" with this concept. I used those twelve oz crappy pepsi max bottles.

What you're talking about is pretty much the concept behind grade school
water bottle rocket launchers.
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Unread postAuthor: FishBoy » Tue Dec 16, 2008 6:57 pm

TapTheForwardAssist wrote:
FishBoy wrote:I made a 3' long (inert) missle which slid over a 3/4" barrel & got some amazing range with it.

edit- link- http://www.spudfiles.com/forums/3-4-car ... 15425.html

(this was it in it's most basic form)


Amazing range? How amazing are we talking here? Now I'm curious!


That toy thing in the link claims to get 1000ft straight-vertical, and those are some tiny 3/4" rockets, and using a really inefficient-sounding gasket-failure trigger system. I'd imagine one could do a lot better with some proper smithing, a 45deg angle, even using the same $2 foam rockets you can buy from that company.

@FishBoy: Your pic is pretty much exactly what I was envisioning. Do you have any longer write-ups, or did you end up giving up on the project?

I won't have time to try and build until January at the earliest (and am also busy writing a thesis and rebuilding a Honda PA50 moped), but would such a creature be pretty easy to build for a novice? It seems to be a pretty standard build, just with a thin/short barrel compared to most. Is it difficult to get sufficient pressure and release it quickly enough to get a good launch?


Well this was made around a wrapping-paper tube which I realized slid perfectly over the 3/4" barrel of my piston valved air gun. The later version was wrapped in black duct tape and had a slightly heavier nose. I only got 2 launches in before losing it however. I would estimate range to be over 100 yards at around 110 psi.
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Unread postAuthor: TapTheForwardAssist » Tue Dec 16, 2008 7:03 pm

You know, that "Airburst" toy is only $21; for something that supposedly shoots 1000' that seems pretty reasonable. I'm almost tempted to buy it, scrap the vertical stand and rig up and angle-shoot bipod and baseplate, and see what it does.

The downside is that the closest/easiest place to shoot it would be the large recreational fields the University maintains a block from my house, but I don't think they have accessible electrical outlets to plug in my air-compressor, so I'd have to use a bike pump.

Though the university wouldn't technically approve of it, since it's just big foam darts I can't imagine that, on the off-chance a security guy wandered by, that it'd be anything worse than "don't do that here."

Image

Note that there's a much smaller version by the same company that claims 500ft, but this one (appears about 1m tall) claims 1000ft.

I'm not finding anything about this model on Spudfiles, has any member toyed with that product before?
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Unread postAuthor: FishBoy » Tue Dec 16, 2008 7:07 pm

You could easily make a much better version of that. That might go 1000 feet, but my experience with anything like that is that they never last for any reasonable amount of time.
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Unread postAuthor: TapTheForwardAssist » Tue Dec 16, 2008 7:16 pm

FishBoy wrote:You could easily make a much better version of that. That might go 1000 feet, but my experience with anything like that is that they never last for any reasonable amount of time.


Ah, thought it'd be too easy.

Could I just build something like this, but with a really narrow barrel to go up in the body of a [s]rocket[/s] dart/quarrel/whatever?

Image


Is that sort of thing well within the capabilities of a novice with basic home-maintenance experience, and basic firearm assembly experience? Also read some stuff about Goyen dump valves that sounded appealing. The system in the above toy sounds shady to say the least, so paying $10 for a fast-acting high-pressure valve sounds reasonable.

Is this sort of thing too funky for a first-timer project? By necking down the barrel so much, would I get some advantage in the airpressure being focused into even a smaller area, or would it contribute to dangerously high pressure in the barrel/spigot?

Forgive my rudimentary knowledge of fluid dynamics.
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Unread postAuthor: FishBoy » Tue Dec 16, 2008 8:32 pm

I would look into modifying sprinkler valves, and then use a 1' or 2' x 1" chamber up to around 130 or 140 psi, and a 3/4" barrel a little bit longer than the planned rocket.
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Unread postAuthor: twizi » Tue Dec 16, 2008 8:40 pm

i made a harpon gun that had a 1/2 barrel and a 3/4 copper pipe witha broad head in it used it for harponing chech out the definition of a harpoon gun
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Unread postAuthor: TapTheForwardAssist » Tue Dec 16, 2008 9:49 pm

FishBoy wrote:I would look into modifying sprinkler valves, and then use a 1' or 2' x 1" chamber up to around 130 or 140 psi, and a 3/4" barrel a little bit longer than the planned rocket.


Huh, so a really long and narrow chamber, rather than the fat ones others use?

Are you envisioning something like 120yds or so with that kind of settup?

Again, I'm not familiar enough with fluid dynamics (or whatever you call it) to understand how changing the chamber shape/size effects the impulse.
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Unread postAuthor: Velocity » Tue Dec 16, 2008 11:14 pm

Clide made a chamber sealing valve cannon that shot toilet paper rolls a while ago; if I find the link in the archives, I'll post it.
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