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valveless/popoff concept

This area is for the discussion of BB or airsoft sub machine guns, and or other small arms such as pellets.
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Unread postAuthor: jackssmirkingrevenge » Thu May 21, 2009 5:41 am

I may be wrong, but I think this is taking striving for minimum part count a few steps too far. It'll be good if it works, and it might to some degree - but I just don't think it's going to work as you want it to.


I understand your qualms, but the performance and efficiency that would result from getting it to work as I intended seem to warrant the effort ;)

Hmm? Sticking BBs to a length of rigid tube with a bit of epoxy? I can think of worse things to do for ammo, hardest bit is chopping the tube to length, then it's just dab and stick.


Fair enough, but still not as easy as just pouring BBs and frankly, custom projectiles are a lot more tracable...

I did something like this long ago. I made a big mag with too many BBs. It had weird air flow problems, the mag became the chamber. I guess a more sophisticated/experienced builder may meet with better results.


Care to share a diagram?
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Unread postAuthor: Hotwired » Thu May 21, 2009 9:35 am

Traceable? You're free to be as cautious about that as you want, I just don't see it working nearly as well with plain bearings.

I'm imagining it to be more of a force-fed cloud strafer, not necessarily a bad thing but it will feed very fast and that's not necessarily a good thing.
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Unread postAuthor: jackssmirkingrevenge » Thu May 21, 2009 10:46 am

Hotwired wrote:Traceable? You're free to be as cautious about that as you want, I just don't see it working nearly as well with plain bearings.


It's a reasonable trade-off in my book.

One could also use these pellets but aside from the lack of stability from an unrifled barrel, they're rather expensive things to be spewing out at full auto.

I'm imagining it to be more of a force-fed cloud strafer, not necessarily a bad thing but it will feed very fast and that's not necessarily a good thing.


With a relatively massive flow to chamber volume ratio, I've seen that a detent can slow things down enough for me to stitch a line of distinct projectile impacts across a target at close range, that's sufficiently lowered rate of fire in my book.

Would the esteemed gentlemen of the board find something like this for 0.177" BBs more agreeable? The mag is 1 BB wide, housed within a 3/4" tube that also serves as a chamber.
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Unread postAuthor: POLAND_SPUD » Thu May 21, 2009 10:56 am

or you can use a hop up unit... or something that works in a similar way

have a look at Subsonic Spuds' gun and its loading mech... this could help to lower ROF as there is no need to provide a lot of air to the chamber since BBs don't have to be agitated

EDIT
of course you would have to put the detent as close the the T as possible - in order to avoid double feeds
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Last edited by POLAND_SPUD on Thu May 21, 2009 11:02 am, edited 1 time in total.
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Unread postAuthor: thedeathofall » Thu May 21, 2009 10:56 am

hhmm.. This second one looks a little more doable.
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Unread postAuthor: jackssmirkingrevenge » Thu May 21, 2009 2:58 pm

POLAND_SPUD wrote:or you can use a hop up unit... or something that works in a similar way


I want something that can hold the projectile to close to 500 psi so which mostly precludes the use of an existing commercial unit.

have a look at Subsonic Spuds' gun and its loading mech... this could help to lower ROF as there is no need to provide a lot of air to the chamber since BBs don't have to be agitated


That's one of the design solutions I'm considering, either with a single stack magazine parallel to the barrel to retain compactness or a multi-row magazine tangential to the barrel as used in the Suomi submachinegun detailed in this patent: http://www.google.com/patents?id=4j5bAA ... dq=2217848
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Unread postAuthor: inonickname » Thu May 21, 2009 6:18 pm

I think that if you want to do this custom ammo is the way.I don't believe you need perfect airtightness, just higher inlet than leakage, but still enough to drop flow enough to allow another round into the breech.

I think a good ammo for this would be to use telescoping tube for the barrel, then get the next (lower) size. Cast some of whatever (a glue) into the pipe, chop it into whatever lengths with a razor saw and mitre box, then a quick pass with a belt sander to finish them off. Or you could just use rod..
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Unread postAuthor: jackssmirkingrevenge » Thu May 21, 2009 11:47 pm

inonickname wrote:I think that if you want to do this custom ammo is the way. I don't believe you need perfect airtightness, just higher inlet than leakage, but still enough to drop flow enough to allow another round into the breech.


Indeed, it would work without a seal in most cases. The thing is that for the small chambers, you'd probably need tiny flow for pop-pop-pop sort of firing so if you want a low rate of fire, the seal would need to be included.

I think a good ammo for this would be to use telescoping tube for the barrel, then get the next (lower) size. Cast some of whatever (a glue) into the pipe, chop it into whatever lengths with a razor saw and mitre box, then a quick pass with a belt sander to finish them off.


This is pretty much what Hotwired was talking about, however as I said for various reasons not worth it in my book.

Or you could just use rod...


... and what better ready made pre-sharpened rods than headless nails :D completely unstable in flight, but at point blank range it wouldn't matter...

Oh dear, look what you've got me thinking!

When I get home I'll knock the heads off a few wall nails and see how far they fly straight from my pengun V2 and what sort of damage they can do at 400 psi, this looks like it could be interesting :D

edit: following some testing, while it would be cool at point blank range it doesn't seem to be worth pursuing.
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Unread postAuthor: psycix » Fri May 22, 2009 1:54 pm

I dont think this is a feasible idea. Your ammo will have to seal very well if you want to have a low ROF, and then the loading mechanism isnt very promising.
I'd call this a modification to a detent vortex.
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Unread postAuthor: skyjive » Thu Oct 01, 2009 6:06 pm

I think this is a great concept, it should give you more efficiency per shot over a traditional auto like a blow forward bolt, while actually being simpler. But you know that already off course.

If you have a lathe it shouldn't be too difficult to make a bunch of custom cylindrical projectiles with an o-ring groove, perhaps at the tail. Just don't lose them when you shoot.

And if you use a spring-loaded detent the advantages are huge. You can adjust spring tension to control firing pressure (and ROF since you can repressurize to a lower pressure faster). But you can also attach a trigger system where you either manually release the detent for semi-auto, or hold down the trigger to allow the spring-loaded detent to cycle for full auto.

The main issue is I think that there will be problems with getting the feed right. Unwanted feeds could be a big problem, with the next round feeding in right after the first one moves out of the way but isn't very far down the barrel, choking off flow. But some fiddling should get it right I think.

Also, to hold a stack of cylinders you're gonna need a rectangular pressure-tight magazine. How is that gonna work?

Edit: Just realized this topic is a lot older than I thought, after following the link. oops.
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Unread postAuthor: POLAND_SPUD » Thu Oct 01, 2009 6:19 pm

yeah... the idea is pretty cool... I don't see much sense in adding o-ring to each projectile really as you can put them on the launcher...

if you could build a prototype that feeds reliably you've got an ultimate gun/holy grail of pneumatic launchers...
:)

lol it's that simple... no launcher could offer such a good performance as this, which is why I think it's not possible to build one that would work all right (if it was then every one, from airgun to paintball manufacturers, would be already using this design)

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Unread postAuthor: jackssmirkingrevenge » Fri Oct 02, 2009 1:38 am

skyjive wrote:Also, to hold a stack of cylinders you're gonna need a rectangular pressure-tight magazine. How is that gonna work?


There are few problems in life that cannot be solved by the judicious application of the appropriate amount of industrial strength epoxy adhesive ;)

lol it's that simple... no launcher could offer such a good performance as this, which is why I think it's not possible to build one that would work all right (if it was then every one, from airgun to paintball manufacturers, would be already using this design)


In some ways, the "BV unit" used in some airsoft guns uses this system, incorporating a reciprocating bolt to aid with feeding.

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Unread postAuthor: jaythedogg » Fri Oct 02, 2009 6:55 pm

I think it can work, but with cylindrical slugs, as I see the advancing pellet's skirt catching on the head of the next one in line.

Cylindrical shaped slugs (for instance .22 LR slugs) & coating each one with Moly lube would make everything move & seal nicely.

(This was directed at the original design concept).
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Unread postAuthor: jackssmirkingrevenge » Sat Oct 03, 2009 2:23 am

jaythedogg wrote:I think it can work, but with cylindrical slugs, as I see the advancing pellet's skirt catching on the head of the next one in line.

Cylindrical shaped slugs (for instance .22 LR slugs) & coating each one with Moly lube would make everything move & seal nicely.


With slugs like that you'd need a rifled barrel, things start to get complicated. Also, lead slugs are hardly reusable, and with an auto you go through a lot of ammunition. This is why I went for 3/8" bearings, though I have to admit they're not as hard as I thought. I have a couple which impacted on a hard surfact that are significantly deformed, if I had enough battery for the macro setting on my camera to work properly I would post pics :roll: :D
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