Unusual Ammo and Barrel Construction

Show us your pneumatic spud gun! Discuss pneumatic (compressed gas) powered potato guns and related accessories. Valve types, actuation, pipe, materials, fittings, compressors, safety, gas choices, and more.
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Lockednloaded
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Wed Mar 03, 2021 12:45 pm

Hi all,

I’ve been away from the forums for a while, but have definitely been tinkering with some old and new projects!

I’m back asking for thoughts on an interesting design challenge I’ve been given. I’ve been asked to design and build a launcher that shoots full bagels...

Now naturally, I could shortcut this with an over sized barrel and wadding, but I wanted to look into more elegant solutions

The powerhouse behind the launcher is a 1.5” QEV piloted with a three-way valve and fed by low pressure CO2. I’m hoping the lower pressures can keep the bagel intact and the velocity low, but I’ve never fired a bagel before

I’m thinking either some sort of strange coaxial barrel to plug the center, or a semi-flattened tube to sling it like a frisbee. Performance isn’t super important (it’s a gun that shoots bagels) but I’ve been unsuccessfully search for anyone who’s tried a similarly weird projectile? Any thoughts or things I might’ve missed before I start shelling out some cash on large diameter pipe and fittings?
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D3moncow
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Wed Mar 03, 2021 4:13 pm

Absolutely love the idea.

A couple of thoughts and questions for the vertical bagel scenario:
-If you would prefer not to do wadding, does that extend to the use of sabots?
-How long of a barrel do you have in mind? Keeping the inner 'guide bar' from drooping (assuming no sabot) would be
a trick on a five foot barrel without the benefit of a front support. It would probably be possible with magnets, such as
the curving ones in an electric motor, but that's pure speculation on my part.
-Are you thinking about muzzleloading or breech loading? The latter would likely be difficult in a vertical orientation, if
you go the guide bar route.

For the horizontal bagel:
-Beyond The Press has done several videos on a rectangular barrel setup, for both frisbees and saw blades. They opted for 3D printed sabots in both cases. The frisbee ended up flipping end over end rather than sailing as if thrown, even when they induced spin.
The frisbee video: https://www.youtube.com/watch?v=xd3HzP8f8po
And the saw blade: https://www.youtube.com/watch?v=228u0IrGgt4

I've only ever used boring circular barrels, alas - no personal experience to add.

As a last, random thought - if you let the bagels go stale for a couple days before firing, you could drop friction by quite a bit at the expense of a good seal. Fresh ones may have enough moisture content to be frozen.
Moo.
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jackssmirkingrevenge
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Wed Mar 03, 2021 4:52 pm

Good to see you!

How about a captive piston?

Imagine a lightweight cup (big yogurt pot?) in a suitably sized barrel.

Critically, the volume of your barrel must be bigger than the expanded volume of the gas in the firing chamber.

This will stop the cup inside the barrel before it exits the muzzle, leaving your bagel to sail on its merry way.
hectmarr wrote:You have to make many weapons, because this field is long and short life
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Thu Mar 04, 2021 12:35 am

You could make a combustion cannon and toast those bagels on their way out! Just kidding, that's probably a terrible idea. Honestly, I think the best option is to build something different. I'm thinking go watch the slingshot channel on youtube and get some rubber-powered ideas to launch the bagels. You could make a really cool bagel crossbow. Using potato gun designs is possible, but tricky to get it right. Using a cup system like JSR said above could work, but that's kind of tricky and reloading could be a pain in the ass not to mention the cost and hassle of CO2 bottles. A rubber-powered crossbow could be easy to use, easy to reload, free and simple to use once it's made and still shoot a bagel hilariously far.
If you are set on using an air or CO2 launcher, then if it were me, I'd look for some rectangular tubing that fits most bagels well and use that for the barrel. Just a simple rectangular tube and don't worry about sealing the bagel in the barrel perfectly or anything like that. The rush of air or CO2 is going to shoot it out plenty fast.
I still say make a rubber-powered crossbow.
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Thu Mar 04, 2021 9:22 pm

Thanks for the inspiration! I've never truly left, but I got a serious engineering job out of school and that's moved me into an apartment and diverted my attention towards some more electronic/computer projects

The more I think of it, the better a "frisbee" orientation seems to me, as far as the questions:

- Wadding: the piece is supposed to be a promo for a friend's bagel shop, so I think a traditional foil wrapping would be my best way to avoid flinging a wadding. I'm hoping to layer the foil to makeup for the lack of uniformity between bagels
-Barrel: no longer than 3 feet. I have a launcher built this size, and I'm trying to keep everything "t-shirt gun" sized for portability
-Loading: in my mind, I'd love to eventually breech load, but I'm going to settle for a muzzle-loader in v1

I think rubber based would make the most feasible sense, but it's a bagel cannon! It should be absurd! Anyways, I have the Co2 setup, and the launcher platform from a previous project, so this will also be the cheapest model if all I'm investing in is the barrel setup.

I like the idea of a captive piston with some serious venting at the front of the barrel. I'm imagining the ports giving it a little better "muzzle flash"

I'll definitely update this thread with what I try and what doesn't work, but I appreciate the inputs!
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jackssmirkingrevenge
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Fri Mar 05, 2021 5:54 am

Lockednloaded wrote:
Thu Mar 04, 2021 9:22 pm
I got a serious engineering job out of school and that's moved me into an apartment and diverted my attention towards some more electronic/computer projects
Been there... it will get better!
I like the idea of a captive piston with some serious venting at the front of the barrel. I'm imagining the ports giving it a little better "muzzle flash"
Here is a very old demonstration of the concept, large diameter barrel coupled with a relatively tiny firing chamber at low pressure.

The plastic cup is very light and forms a parachute seal against the sides of the barrel.



As you can see, the simple fact that the expansion behind the cup lowers the pressure in the barrel to less than atmospheric pressure is enough to stop the cup before it leaves the muzzle, while the projectile flies free.
hectmarr wrote:You have to make many weapons, because this field is long and short life
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Fri Mar 05, 2021 10:10 am

jackssmirkingrevenge wrote:
Fri Mar 05, 2021 5:54 am
Lockednloaded wrote:
Thu Mar 04, 2021 9:22 pm
I got a serious engineering job out of school and that's moved me into an apartment and diverted my attention towards some more electronic/computer projects
Been there... it will get better!
I like the idea of a captive piston with some serious venting at the front of the barrel. I'm imagining the ports giving it a little better "muzzle flash"
Here is a very old demonstration of the concept, large diameter barrel coupled with a relatively tiny firing chamber at low pressure.

The plastic cup is very light and forms a parachute seal against the sides of the barrel.



As you can see, the simple fact that the expansion behind the cup lowers the pressure in the barrel to less than atmospheric pressure is enough to stop the cup before it leaves the muzzle, while the projectile flies free.
It is impossible to stop thinking about what the captive piston can suck, due to its inertia mass, from the back, after expelling the projectile, perhaps a measure of combustible gas. 8-)
I had no idea about this kind of technique, it seems simple to me and it works very well.
I am the author of the first semi-automatic hybrid, check this out :shock: ...viewtopic.php?f=28&t=26676
And of the hybrid that can shoot in the shortest time: :shock: viewtopic.php?f=28&t=27190
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Fri Mar 05, 2021 11:29 am

hectmarr wrote:
Fri Mar 05, 2021 10:10 am
It is impossible to stop thinking about what the captive piston can suck, due to its inertia mass, from the back, after expelling the projectile, perhaps a measure of combustible gas. 8-)
I had no idea about this kind of technique, it seems simple to me and it works very well.
With the same combination of a high barrel to chamber volume ratio, you can observe this effect in combustion type launchers as well.

Here is a demonstration I had made with a tennis ball in a transparent tube:



I would say it actually works better because the gasses contract once they start to cool.
hectmarr wrote:You have to make many weapons, because this field is long and short life
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Fri Mar 05, 2021 12:04 pm

I agree. As the gas cools, it contracts and takes up less volume.
In fact, if you add a spring to the front of the barrel, so that the captive piston goes back to where it all started, it could be used as a mixer perhaps for a combustion gun.
When you inject the compressed air, the piston tries to come out, compressing the front spring. On its way, and when the pressure is negative, by inertia, it sucks a certain volume of fuel gas, through a one-way valve that opens into the tube.
After this, the spring returns the captive piston to the beginning and injects the mixture into an explosion chamber of a combustion weapon.
The regulation of the inertial system is determined by the mass of the piston, the force of the spring. It's just my opinion, at first glance.
I am the author of the first semi-automatic hybrid, check this out :shock: ...viewtopic.php?f=28&t=26676
And of the hybrid that can shoot in the shortest time: :shock: viewtopic.php?f=28&t=27190
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Fri Mar 05, 2021 2:53 pm

"if it only fires one shot I am not interested"
Classic Hector :D

I think we had started down that road here...
hectmarr wrote:You have to make many weapons, because this field is long and short life
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Fri Mar 05, 2021 3:33 pm

Héctor clásico :D
:lol: :lol: :lol: you made me laugh.
I am the author of the first semi-automatic hybrid, check this out :shock: ...viewtopic.php?f=28&t=26676
And of the hybrid that can shoot in the shortest time: :shock: viewtopic.php?f=28&t=27190
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Sat Mar 06, 2021 6:46 am

A skeet launcher comes to mind
GettyImages-1174255328.jpg
This might be worth a look :P
0rsi1lk1epf61.png
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Tue Mar 09, 2021 4:29 pm

I ordered some parts today, and I think I have a pretty good plan! The Co2 system and 3-way valve have been working well, so the easy part is out of the way.

For the barrel, I ordered some rectangular aluminum tubing 5" wide x 2" tall. This should fit most of the bagels I have in mind, and to create a better seal--I'll be doing some custom filleting of the inner corners. I hope to accomplish this with quartered PVC inserts, but if that doesn't work, I have already mocked up some 3-d printed inserts to run along the length of the barrel.

Plan C would be to 3D print some rectangular cup sabots in vase mode. I would hope that they'd stay captive, but I'll over compensate by making them disposable and too lightweight to cause any collateral damage

If these methods are successful, the stretch goal would be to run a rubber "hop-up" on one side of the barrel. I'm hoping that some gasket material at the last bit of the material will impart a little bit of spin, but I guess we'll see...

Distance is really not a huge issue, since the launcher platform should have more than enough power (pretty overkill really, but it's what I had on hand)

I'm excited to integrate some 3D printing in the barrel supports and fillet adapters--merging an old hobby with a new one!
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Tue Mar 09, 2021 10:23 pm

Sounds promising. Can't wait to see the build take shape.
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Wed Mar 10, 2021 7:59 pm

Update: I no longer know how to post pictures properly, but I’ve made progress on the build

https://imgur.com/gallery/PcKwkWa

Here’s an album of some detail shots of the barrel. All the parts are printed in ABS, but aren’t holding any significant pressure here. I won’t add the fillets into the barrel until after testing a few bagels without them. Hopefully they’ll be unnecessary for the performance I’m looking for, but I still think they look pretty cool

I offset the adapter in order to fit it around the existing cannon, but maybe there’s a chance it’ll give me some fun spin?
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