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"valveless" cartridge concept

A place to ask general spud cannon related questions.
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Unread postAuthor: jackssmirkingrevenge » Mon Nov 01, 2010 1:37 am

saefroch wrote:Any idea what pressure it's popping at, and if you can get it to pop pretty close to 800psi?


According to my tests here with the same kind of seal, it's popping at around 200 psi so there certainly is room for improvement. I'd have to do some tweaking to up that, maybe by crimping the end of the cartridge as suggested here.

Oh don't forget that you can delay the bolt with the use of a simple check valve


This still applies :wink: the way it is I don't think there will be any need to delay the bolt, just increase its travel and that should allow enough time for a new projectile to feed into the breech. I'm sure there will be a lot of blood, sweat and tears involved in making that reliable but it's certainly not impossible.

For those of you who do not share my obsession with flying brass, this could also be made to work more efficiently without the use of cartidges-
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Unread postAuthor: maverik94 » Mon Nov 01, 2010 9:57 am

For those of you who do not share my obsession with flying brass,

Haha. Isn't that what every airgunner secretly desires? To get ice burns on their arm from flying air cartridges? :D Speaking of which; are those cartridges cold when they're spent?
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Unread postAuthor: Technician1002 » Mon Nov 01, 2010 10:08 am

I like your basic layout of the autoloader. Under close examination, it will need a change in the trigger/air source.

With just a blow gun, when the shot is fired, and the plunger pushes back, if the air is still on, the pressure will lower the collum of rounds preventing feeding.

A small chamber with a high flow hammer valve could make it work with a properly massive plunger. The chamber would pop through the hammer valve and discharge the round and then close. The pressure pulse would have imparted KE and momentum to the plunger which continues moving even in the lack of chamber pressure/closed hammer valve. This would leave the pressure away from the magazine so it would spring load the next round and the plunger finishes it's loading cycle for the next shot.

I may see if I can add a golfball magazine to a QDV cannon to auto load golf balls from a magazine this way. It is a good basic design. Thanks.
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Unread postAuthor: jackssmirkingrevenge » Mon Nov 01, 2010 11:19 am

maverik94 wrote:Isn't that what every airgunner secretly desires? To get ice burns on their arm from flying air cartridges?


It's not universal though, for example 100% of all Polish spudgunners I've spoken to think it's a childish waste of time :D

are those cartridges cold when they're spent?


I don't know at what temperature it ejects but by the time I friggin' find it it's at room temperature :roll:

Tech wrote:I like your basic layout of the autoloader. Under close examination, it will need a change in the trigger/air source.

With just a blow gun, when the shot is fired, and the plunger pushes back, if the air is still on, the pressure will lower the column of rounds preventing feeding.


Not necessarily, first of all having the magazine tube say 1/8" wider than the projectiles will prevent this effect because the pressure in the tube will equalise.

Also, if you don't use "just a blowgun", you would be negating the whole advantage of using the valveless/pop-off principle, which is basically getting performance better than a piston valve using only a rudimentary trigger valve.

The theory is that you open the blowgun and the pressure builds up, sealing the projectile in the breech against the seal and pusing the bolt back. Bolt spring compression should be set so that the projectile pops around the time the bolt passes over the magazine.

Once the bolt is past the magazine, a new projectile rises into the breech while the bolt continues to travel back by its own momentum. The bolt then stops and reverses, pushing the new projectile into the seal.

The trick is to balance bolt weight/spring compression to allow the above cycle to happen, once that is achieved I see no reason why it shouldn't work as described.

I may see if I can add a golfball magazine to a QDV cannon to auto load golf balls from a magazine this way. It is a good basic design. Thanks.


I would really like to see someone do this in a larger calibre, with the construction techniques you've applied to spudguns it should be very achievable - just make sure you build in "tweakability" in the bolt setup, you'll need it!

As to the subject of this thread, I'm going to extend the bolt tube in order to fit a compression spring, so instead of the wire stop I can allow the bolt to travel further back allowing enough time to feed another round, watch this space :)
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Unread postAuthor: Technician1002 » Mon Nov 01, 2010 12:00 pm

I have been toying with the idea of a magnet on the bolt and a copper damping ring the magnet would extend into at the end of the rearward travel. It would both apply dynamic brakes at the end of travel and hold it open for a short time to allow a round to load.
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Unread postAuthor: POLAND_SPUD » Mon Nov 01, 2010 12:14 pm

Technician is right - it might be tricky to get it to work right. Some of these problems can be solved simply by turning this into a hybrid. In fact this design is pretty much the thing I designed for the hybrid I am building.

The cool thing about it is that you can easily use it on coaxil guns
[youtube]http://www.youtube.com/watch?v=Wh2mjng8848&feature=related[/youtube]

As you can see it is possible to build a breech loaded coaxial
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Unread postAuthor: jackssmirkingrevenge » Mon Nov 01, 2010 3:39 pm

POLAND_SPUD wrote:Some of these problems can be solved simply by turning this into a hybrid.


Of course cartridges are an overcomplication, but we can make things easier by throwing in fuel mixtures and ignition. Seriously, does "simple" mean something else in Polish :D
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Unread postAuthor: POLAND_SPUD » Mon Nov 01, 2010 4:51 pm

No, but we still don't know whether it works with a magazine or not. Tech explained it quite well so I don't see any sense in paraphrasing his words.

I am jsut a bit worries as the bolt might essentially turn into one of your failed farting machines after the first shot.

The simplest way to avoid this risk is to add a valve that cuts off air supply as till the bolt returns to its original position...

...or converting it into a hybrid[/b]
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Unread postAuthor: saefroch » Mon Nov 01, 2010 5:41 pm

Has nobody considered putting a f*cking powerful spring at the bottom of the mag so that even if the mag is at max pressure, it'll still load another round?
:idea:
Or you could just place a sizable hole in the bottom of the mag, and move that bolt o-ring onto the bolt itself...
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Unread postAuthor: jackssmirkingrevenge » Mon Nov 01, 2010 11:49 pm

POLAND_SPUD wrote:I am just a bit worries as the bolt might essentially turn into one of your failed farting machines after the first shot.


First of all I was really aiming for semi auto with this thing, it goes full auto then well and good but it's not the main aim.

In any case though, I see no juncture where it should become a farting machine because the barrel is "open" when the new cartridge is being fed so there should be no significant pressure buildup in the breech preventing the new cartridge being seated.

If you're referring to the "caseless" design posted on this page, the same logic applies because before the projectile goes past the valve porting into the breech, there is no reason for any pressure buildup because air coming from the blowgun will be vented through the barrel, so no reason for flatulence there ;)

The simplest way to avoid this risk is to add a valve that cuts off air supply as till the bolt returns to its original position...


I could easily have avoided the whole pop-off cartridge thing by grafting this to my original cartridge design but I think the current prototype is a better way of doing things.

New bolt setup is cured and I'll test it after work, if I can get it cycling nicely I'll rustle up some more cartridges and a magazine and see if this will actually feed itself :)
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Unread postAuthor: POLAND_SPUD » Tue Nov 02, 2010 6:37 am

I could easily have avoided the whole pop-off cartridge thing by grafting this
Lol in case you haven't noticed... Your design is Rattlesnake V3 - HPA auto valve... there are some differences but the operating mechanism is the same...
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Unread postAuthor: jackssmirkingrevenge » Tue Nov 02, 2010 7:17 am

POLAND_SPUD wrote:Your design is Rattlesnake V3 - HPA auto valve... there are some differences but the operating mechanism is the same...


You can say that, but at least in this case the cartridges are actually contributing to the function :) couple of hours of work left and I'll test it as a multishot :D

Edit: Here's a test of the cartridge ejecting with the new breech, with the target - a CD in this case - is visible being struck in the background. Time to make a magazine and some more cartridges :D

[youtube]http://www.youtube.com/watch?v=xCAucmpY0NQ[/youtube]

Edit 2: I made the magazine a little too tight and it's causing too much friction with cartridges fitted so I'm going to have to redo it, but tested it with a rubberband sprung balsa wood follower and it's looking *very* promising, the follower snapped into place before the bolt came back, if that was a cartridge it would have most likely been fed into the breech :D

[youtube]http://www.youtube.com/watch?v=ESFY7dezLzw[/youtube]

Edit 3: Getting there, but not quite...

[youtube]http://www.youtube.com/watch?v=F3EzcIZPoDI[/youtube]

The potential solution is a heavier bolt, increasing bolt travel and reducing spring pre-compression, giving the bolt a really good run up so it can smack the new cartridge into the breech.
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Unread postAuthor: ramses » Tue Nov 02, 2010 8:51 pm

:shock: :shock:

GREAT work! This has huge potential for flying brass goodness. And it works! :D
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Unread postAuthor: saefroch » Tue Nov 02, 2010 9:08 pm

You know... you could just loop that last vid :wink:

EDIT: or you could try increasing the slide room for the bolt to allow the next cartridge to settle before the bolt slams into it...
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Unread postAuthor: jackssmirkingrevenge » Wed Nov 03, 2010 1:23 am

ramses wrote:GREAT work! This has huge potential for flying brass goodness. And it works! :D


Cheers :) actually the fact that it's only popping off at around 25% of the pressure I'm feeding it means there's a lot more power potential, both in terms of projectile as well as power available to the spent cartridge to work the breech.

You know... you could just loop that last vid ;)


:D :D :D

or you could try increasing the slide room for the bolt to allow the next cartridge to settle before the bolt slams into it


The problem isn't that the next cartridge doesn't have time to move into place, but the bolt itself doesn't have enough cojones to push the cartridge into the breech.

My plan therefore as in my previous post is to extend the bolt spring housing, which reduces spring pressure on the bolt while allowing it to slide back further, the idea being that it will build up more momentum and bodily smack the cartridge into the breech when it returns.
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