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"valveless" cartridge concept

A place to ask general spud cannon related questions.
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Unread postAuthor: ramses » Wed Nov 03, 2010 5:03 pm

saefroch wrote: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...



:D :D


Or you could build a delayed-blowback mechanism. :roll:

How are you keeping the mag from just dumping it? I don't see any lips on the mag, or a "top" on that breech.
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Unread postAuthor: POLAND_SPUD » Wed Nov 03, 2010 7:02 pm

Something along these lines would fix the problem and reduce air consumption at the same time. The only problem is to find a valve that can handle 800 psi
[youtube]http://www.youtube.com/watch?v=OVR-beHcyOw[/youtube]

EDIT
Oh before anyone asks I mean the mechanical valve that cuts off air supply as soon as the bolt retracts, not the air cylinder (though not that you can't use it... but Im pretty sure JSR won't do that)
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Unread postAuthor: Lockednloaded » Wed Nov 03, 2010 10:15 pm

Thats a cool concept POLAND_SPUD, idk how you could implement it into an actual launcher. Was this idea loosely based on a popular fire-arm conversion that turns semi-auto blow-back pistols into full-auto? they both work in similar ways.
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Unread postAuthor: jackssmirkingrevenge » Thu Nov 04, 2010 1:40 am

ramses wrote:How are you keeping the mag from just dumping it? I don't see any lips on the mag, or a "top" on that breech.


Does this picture of the current setup answer your question?

I've done extensive testing and it doesn't seem it's going to work as is - in order for it to work, the o-ring seals in the breech are unavoidable, and they entail a certain amount of friction which the bolt has to overcome in order to chamber the next round properly. If I make the bolt strong enough to do this however, the cartridge then doesn't have enough energy to overcome the bolt stength and eject itself.

POLAND_SPUD wrote:Oh before anyone asks I mean the mechanical valve that cuts off air supply as soon as the bolt retracts, not the air cylinder


That would help with air efficiency but not with the function of the bolt, the fact that air supply is continuous is not the reason that it doesn't rechamber, it's mostly the friction as stated above.

Potential solutions include:

- increasing cartridge diameter, this will not only increase "chamber volume" but also provide a greater surface for the air pressure to push on and eject the cartridge. I'm toying with the idea of using spent 7.62mm brass for this, my only gripe is cartridge shape consistency when it comes to sealing the in breech.

- increasing pop-off pressure from the current approximate 200 psi, this would entail a certain amount of fiddling with materials though and is a sweet spot of pop-off pressure that is not easy to achieve without adjustable seals in threaded fittings.

- accepting that rechambering a fresh cartridge is not really a design requirement, and I would probably be happy to fire one shot and watch the cartridge eject, then manually push the bolt forward to load a new cartridge for the next shot. This would make full auto impossible (unless you use some externally powered bolt like our Polish comrade suggested, but as he correctly predicted this is beyond the complexity level I'm willing to tolerate :roll:) but there are BBMGs for that ;)

A bit more musing is in order, also following my recent experiences with a larger bore hybrid I'm thinking of marrying something the size of my combustion cartridge experimentation with low mix burst disk cartridges and make a big f***-off XM109 style launcher.

So many projects, so little time!
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Unread postAuthor: POLAND_SPUD » Thu Nov 04, 2010 8:00 am

it's mostly the friction as stated above
Well if it is friction then get a stronger spring

make a big f***-off XM109 style launcher.

lol why stop there ?? :D
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Unread postAuthor: jackssmirkingrevenge » Thu Nov 04, 2010 8:28 am

POLAND_SPUD wrote:Well if it is friction then get a stronger spring


Ah, but:

JSR previously wrote:If I make the bolt strong enough to do this however, the cartridge then doesn't have enough energy to overcome the bolt stength and eject itself.


POLAND_SPUD wrote:lol why stop there ?? :D


Believe me, if I had the space I would have made a full size hybrid '88 replica ages ago! I might consider something a bit more sci-fi like the Standard Issue Big Gun previously proposed in the community project (several) pipe(s) dream :)
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Unread postAuthor: POLAND_SPUD » Thu Nov 04, 2010 8:36 am

Ah, but:

what if you used air to push the bolt back in place ? More less using the same method that I posted above?

ohh well forget about it - I know what you're going to say.... too complicated
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Unread postAuthor: jackssmirkingrevenge » Thu Nov 04, 2010 9:15 am

POLAND_SPUD wrote:what if you used air to push the bolt back in place ? More less using the same method that I posted above?

ohh well forget about it - I know what you're going to say.... too complicated


Actually, this time you might actually have a point, hmmm...

edit: added a check valve to make sure there's enough air for it to work
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Unread postAuthor: Fnord » Thu Nov 04, 2010 9:31 am

Hell jsr, that would be easy.^

Striking the pin of a schrader or quick-connect in a tube with the bolt might be enough, though you might have to be particular about where you put your exhaust holes.

We need to get you some quick-set epoxy.
(No, really. Quick set for prototypes, Regular for finished products.)

However I'd try increasing the pop-off pressure first. And greasing up the breach.
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Unread postAuthor: jackssmirkingrevenge » Thu Nov 04, 2010 12:18 pm

Fnord wrote:Striking the pin of a schrader or quick-connect in a tube with the bolt might be enough, though you might have to be particular about where you put your exhaust holes.


I have experience of using a schrader as a hammer valve with this project so that might be a good idea, as to exhaust holes I figure having the bolt that is a 6mm o/d tube riding in a 6mm i/d tube will make it an efficient "projectile" to ram the fresh cartridge into the breech and not having it perfectly sealed means that the air can vent past it once it seats.

However I'd try increasing the pop-off pressure first. And greasing up the breach.


The breech and cartridges are already well greased, and increasing pop-off pressure would of course be ideal - it would increase muzzle energy (currently borderline acceptable, especially considering I'm feeding the thing 800 psi!) as well as negating the need for wasting air to reseat the bolt.

I tried to compressed the seal by adding a chamfered tube for my cartridge project like so:

Image

Hooked up to my paintball tank at 800 psi the BB failed to pop though.

What I can do is try to crimp the mouth of the cartridge incrementally like so and see if that makes a difference, maybe using a drill chuck or by forcing into a suitable conical bore.
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Unread postAuthor: POLAND_SPUD » Thu Nov 04, 2010 1:01 pm

heh that's exactly what I meant :D

However, the beauty of this design was its simplicity...
hmmm I've got to think more about it

ohh btw 'polski mod' was correct.... 'zmiana polskiego' is not... (adjectives come before the noun - just like in English)
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Unread postAuthor: jackssmirkingrevenge » Thu Nov 04, 2010 1:11 pm

surely some kind of impostor wrote:However, the beauty of this design was its simplicity...


:shock:

I never thought I'd live to hear you make such a statement :D

ohh btw 'polski mod' was correct.... 'zmiana polskiego' is not... (adjectives come before the noun - just like in English)


I made the effort to ask google translate, don't blame me if it wasn't up to the job :P :D
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Unread postAuthor: POLAND_SPUD » Thu Nov 04, 2010 1:39 pm

well, it seems that you speak better polish than google translate :D

anyway... have you considered adding another shrader that cuts of air supply as soon as the cartridge is ejected ?? well if you've got to make it more complicated then at least make sure it is better


lol at least now you realise why I said it would be a good idea to turn it into a hybrid...

EDIT

POLSKA_HYBRYDA :wink:
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Unread postAuthor: jackssmirkingrevenge » Thu Nov 04, 2010 1:44 pm

POLAND_SPUD wrote:have you considered adding another shrader that cuts of air supply as soon as the cartridge is ejected ?? well if you've got to make it more complicated then at least make sure it is better


I don't see the benefit of cutting off the air supply, it won't help with rechambering the cartridge and I think the benefits in air economy would be minimal.

lol at least now you realise why I said it would be a good idea to turn it into a hybrid..


Fair point! Though now that I think about it, hammering the cartridge nose first into a tapered bore should be a good way to increase pop-off pressure, still at work but I'll give it a go when I get home, before I make any radical modifications to the breech and action.

edit: here's the v1.1 cartridge with a crimped nose (down to 5.4mm from the original 6) by hammering it into the fitting illustrated, and a 5.56mm cartridge for scale ;) I don't know how much of a difference it will make, watch this space
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Unread postAuthor: Gun Freak » Thu Nov 04, 2010 4:21 pm

I think you should go for a higher pop pressure and a larger cartridge diameter, more power and enough recoil to eject. My thoughts on non-semi auto... I say you go for semi. You came this far for a cart ejecting semi, why give in to this problem and settle for not even semi. You are JSR, my friend, you can find a way to make a stronger bolt :)

K I wrote all that before finishing reading the thread, good luck with the new test.
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