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"valveless" cartridge concept

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Unread postAuthor: jackssmirkingrevenge » Wed Jul 14, 2010 2:55 pm

Ragnarok wrote:In fact, I think it would probably eject very violently. If you look, after it starts moving back, the entire frontal area of the cartridge is exposed to pressure, which means there'll actually be more force on the cartridge than the projectile.


Precisely, it's the same sort of stepped piston concept which pop-off valves use, as noted earlier on ;)

I've been thinking, perhaps the spring injector can be eliminated altogether and have the cartridge feed through side porting, in this way while it is being pressurised it will not move, until the projectile is released. Basically a combination of myoriginal cartridge prototype with the pop-off concept.

Also, provided that the air feed port is significantly smaller than the barrel diameter, therefore not providing a net force on the next cartridge feeding into the breech, it should continue to fire as long as air continues to be fed and there are cartridges in the magazine.

Finding the correct balance between sealing and friction would be crucial though, it doesn't need to be a 100% seal though as long as any leaks are minimal compared to the trigger flow.
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Unread postAuthor: Dave_424 » Wed Jul 14, 2010 3:26 pm

Jack, We might be thinking along the same lines....

Im about to start another project using either the BACS cartrige system (I know you know what I'm on about)

Working off a .50 BMG (I don't have one to work off but I'm sure I can find the dimentions off the net)

Ammo will be commercially avaiable paintballs for ease but could cast some mean looking slugs.

I was going to go with Bolt action (Good practice for gunsmithing which I want to go into) but COULD be pursuaded to go with semi auto if you can convince me that there would be enough force to work the action.

Pressure will be anything up to 200 BAR depending on the burst pressures of the cartriges when the final design is chosen.

Everything will be machined and won't be a drop of epoxy in sight :D

Dave
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Unread postAuthor: ramses » Wed Jul 14, 2010 3:34 pm

That looks acceptable and much simpler, but it requires that you keep your cartridges clean. Which will be require active cleaning, seeing that they will be shooting all over the place.

Achieving a good seal should not be a problem, so long as you can make female O-ring grooves. You could even use floating O-rings. Perhaps that will need machining.

The risk of jamming should be about the same, but if you compromised with the side ejecting and ejected out the top using the spring force applied from the mag to the next cartridge, it would be less likely to jam. I really like side ejecting and bottom feeding, though.

It seems this is even better suited to using firearm cartridges than the previous version; you just need to cross drill and epoxy in a seal in the neck of something like a 30-06. That would complicate the breech (require a taper), but simplify cartridge construction. It's probably easier to make a jig to glue in seals than machine a fairly precise taper into that breech. Unless you cast the taper after the grooves were machined.

I think deciding on the easiest way to make this is harder than the hardest reasonable method.

Oh, and if you cut off airflow based on bolt position, you could have a larger air input, and MOAR ROF.
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Unread postAuthor: jackssmirkingrevenge » Wed Jul 14, 2010 3:54 pm

Dave_424 wrote:Im about to start another project using either the BACS cartrige system (I know you know what I'm on about)


For semi-auto I would exclude the BACS design altogether, too limited in terms of flow.

My experimentation with co-axial designs iswell documented, and for all my efforts I don't think they are a good idea for blowback either - limited chamber volume and the added weight and complexity of a filling valve makes such cartridges heavy, delicate and requiring a substantial hammer strike to open them.

This is why I think the above design has such promise - an extremely basic and light cartridge, with the ultimate zero opening time/maximum flow performance.

Everything will be machined and won't be a drop of epoxy in sight :D


You're lucky to have that luxury ;)

That looks acceptable and much simpler, but it requires that you keep your cartridges clean. Which will be require active cleaning, seeing that they will be shooting all over the place.


If I had a working semi/full auto cartridge fed design, I think giving cartridges a quick wipe-down would be par of the joys of using it :)

The risk of jamming should be about the same, but if you compromised with the side ejecting and ejected out the top using the spring force applied from the mag to the next cartridge, it would be less likely to jam. I really like side ejecting and bottom feeding, though.


The performance potential of HPA + valveless design should mean sufficiently violent blowback for reliable functioning.

Achieving a good seal should not be a problem, so long as you can make female O-ring grooves. You could even use floating O-rings. Perhaps that will need machining.


I can cast the breech around a cartridge blank with a couple of o-rings slipped over it, no worries there - I had done something similar for this detent. I don't think using firearm cartridges is a good idea, most of the ones in my collection are recovered ones of which very few are in perfect shape.

I think deciding on the easiest way to make this is harder than the hardest reasonable method.


As with any project. I would much rather find the simplest way of doing things, regardless of the mental effort, instead of embarking on a complicated project then realise that I could have done things differently.

Oh, and if you cut off airflow based on bolt position, you could have a larger air input, and MOAR ROF.


Good point, though in this case ROF isn't really what I'm after.
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Unread postAuthor: Gun Freak » Wed Jul 14, 2010 4:08 pm

Looking forward to a prototype Jack, this could be really awsome. :thumbleft:
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Unread postAuthor: Dave_424 » Wed Jul 14, 2010 4:12 pm

Good points Jack, I already kind of changed my mind :D

Now going with an air rifle design based off probably the Theoben Rapid because it is easy to work with aluminium block.

Ive got some DOM tubing on the way and also a paintball barrel on it's way.

I might do a build log if Im not too lazy.

I love gloating about precision machine tools, However I don't have a Less than amazing chinese lathe, good, old, heavy english lathe :D

Dave
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Unread postAuthor: POLAND_SPUD » Wed Jul 14, 2010 4:18 pm

this one looks a better... but I still think that cartridges make little sense... while I could accept them in a hybrid they make little sense for pneumatics

anyway today I decided to make a 'good' video... I completely obliterated a 2L bottle filled with water with no stoppages whatsoever... only to discover that the camera didn't record it... ohhh well

but I did film this later on... not very impressive due to lotzzz of stoppages but I think you'd like how phallic the target is/was
[youtube]http://www.youtube.com/watch?v=zB4_7I-V52U[/youtube]


so forget about cartridges and find a way to improve feeding on valveless guns
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Unread postAuthor: jackssmirkingrevenge » Wed Jul 14, 2010 4:26 pm

POLAND_SPUD wrote:this one looks a better... but I still think that cartridges make little sense... while I could accept them in a hybrid they make little sense for pneumatics


As I might have mentioned before (:roll:) I am the proud owner of a 30 ft/lb semi-automatic 0.22 air rifle, so attempting to make a home-made launcher with probably lower performance and doubtless *much* less accuracy - definitely not 2" groups at 120 metres material - does not seem worth the effort.

If I can get reasonable power (10-15 ft/lbs) and flying brass, that's a project worth making :)

I think you'd like how phallic the target is/was


lol, it looks like an aroused jolly green giant was buried in your garden and you ruined his day :D

Quite impressive, shame about the lack of reliable feeding.

Have you considered a vortex design?

I might just have to make one to shut you up :D ;)
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Unread postAuthor: POLAND_SPUD » Wed Jul 14, 2010 4:34 pm

Have you considered a vortex design
I am going to test it soon... if that fails I'll build a simple tube mag
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Unread postAuthor: psycix » Wed Jul 14, 2010 4:58 pm

Nice one on the seals :lol:

Looking at how you like flying brass you must really hate revolver type guns, maybe even more then seals.


Why not just actuate the cartridge mechanism with a pneumatic ram? Mix up poland's semi with your cartridges.
Then slap on a popoff or something like that to make it fully automatic.
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Unread postAuthor: jackssmirkingrevenge » Wed Jul 14, 2010 5:18 pm

POLAND_SPUD wrote:if that fails I'll build a simple tube mag


Remember this one?

My u-bend skills were composed mostly of fail, so it didn't work, but if you could get properly bent tubing in a "U" shape along the length of the barrel, just two lengths along the barrel, ie starting at the breech, going to the muzzle and coming back to the breech - for say a 50cm barrel would give you around 165 6mm rounds (or 220 4.5mm rounds ;)), without any mags sticking out or adding length.

Looking at how you like flying brass you must really hate revolver type guns, maybe even more then seals.


Revolver-type launchers would be a real headache given my lack of machine shop facilities, so I would tend to give them a wide berth.

I like this one though ;)

Why not just actuate the cartridge mechanism with a pneumatic ram? Mix up poland's semi with your cartridges.
Then slap on a popoff or something like that to make it fully automatic.


The idea here is to simplify the design... Though after having got this mechanism to work, I'm sure adding a QEV + popoff + HPA would give it worthwhile power. That would be my last resort though ;)
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Unread postAuthor: ramses » Wed Jul 14, 2010 9:19 pm

I don't think using firearm cartridges is a good idea, most of the ones in my collection are recovered ones of which very few are in perfect shape.


You could, as silly as it sounds, buy them. If you feel like spending a bit more, they will actually clean, de-prime, trim and re-size them for you.

If you want go go for broke you could use these Scroll down even further, and you can buy some APIT (Armor Piercing Incendiary Tracer) rounds for them!


That first place also sells shotgun hulls

Even though I have a lathe, it is usually easier to JB weld tiny things together instead of threading them. Or when whatever I am making a finishing cut on inevitably decides to get knocked out of concentric in the chuck, bend the 1/4" semi-hardened drill rod, and shear off the 8-32 threads holding it together. That is to say, the 8-32 threads in the hole I re-tapped after having the EXACT same thing happen with 5-40. :D
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Unread postAuthor: jackssmirkingrevenge » Thu Jul 15, 2010 12:34 am

You could, as silly as it sounds, buy them


Not as easy as it sounds due to the strange laws governing epoxyland, where skillfull and well trained customs officials are unable to distinguish between a spent cartridge, loose bullet or a complete live round :roll:

Anyway, prototype. I don't think I can simplify things more than this, so it seems I have some casting to do this evening, and not in the Pierre Woodman sense :roll: :D
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Unread postAuthor: ramses » Thu Jul 15, 2010 11:38 am

customs officials are unable to distinguish between a spent cartridge, loose bullet or a complete live round


You could have it labeled scrap brass... or "historical artifacts" or "look ma, No gunpowder! I guess I'm just partial to ejecting real brass.
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Unread postAuthor: jackssmirkingrevenge » Thu Jul 15, 2010 12:11 pm

I guess I'm just partial to ejecting real brass.


I'm just after a realistic clatter, no need for real brass for that ;) but continue reading, this will make it even easier to use actual cartridges:

I've been doing some more thinking after grabbing some materials, and I think I've hit on a way to make it even more likely to function reliably. I've removed one of the chamber seals, and moved the projectile seal from the cartridge mouth to the chamber breech.

This way, the cartridge will start to blowback before the projectile is fired. It will need some fine tuning to get projectile exit and blowback timed right, but that should just be a question of altering spring strength, ie more compression if the cartridge ejects without firing the projectile, less if the projectile fires but the cartridge doesn't eject.

It also makes the cartridge seal-free and therefore there is nothing to wear out.

Apologies for the incomplete cycle, I've had a long day at work and I couldn't be arsed staring at the monitor finishing the animation, time I could spend playing with epoxy
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