SpudFiles

You really have no concept whatsoever of "keeping things simple" eh

While what you suggested could conceivably work, it's much less complicated to add weight to the bolt. If it works for the Sten-M3-MP40-Uzi-MAC-10-every other direct blowback submachinegun I can think of, why not

so it reduces the chance of injury

I think I'd be in greater danger of being struck by a spent cartridge...

When are we going to see a polish hybrid

You really have no concept whatsoever of "keeping things simple" eh

Something tells me that our understanding of what is simple differs a lot

ohh well time will tell

When are we going to see a polish hybrid

when I finish it and then achieve world domination you'll regret this comment! ...haha...muhahahaa!

POLAND_SPUD wrote:Something tells me that our understanding of what is simple differs a lot

Fair enough, but surely simply adding weight to a bolt is an easier proposition than having a sealed piston bolt with a check valve...

One thing I think I will have to do is increase bolt travel, as it is the spring reaches maximum compression a couple of mm after the ejector. Testing will tell, having a high speed camera to evaluate the dynamics of the system will be really useful in this case

when I finish it and then achieve world domination you'll regret this comment! ...haha...muhahahaa!

It seems we have the same plans

edit: Fail, the first shot blew off the barrel for some reason sadly no footage of that happening, but here, just for the sake of having the first cartridge ejecting hybrid on spudfiles, here's the stumpy remains in action at 6x:

[youtube][/youtube]

edit 2, some more videos at 1000 fps:

*this* is the ejection I want to see

[youtube][/youtube]

[youtube][/youtube]

:wav:

Awesome job. Glad to see you secured the launcher better. Now you just need to epoxy the barrel back on, make a mag and about 10 more cartridges, and it'll be awesome (er)!

Maybe you could use a copper barrel and solder it in...

OLE!
Great job, did you take the spring out in the last videos? Perfect ejection. Nice.

wow im kinda wishing i was making one of those but maybe for my next gun if i feel up to it, but anyway great work cant wait to see it with a mag, you started making any more cartridges yet?

ramses wrote:Awesome job. Glad to see you secured the launcher better. Now you just need to epoxy the barrel back on, make a mag and about 10 more cartridges, and it'll be awesome (er)!

Cheers I intend to repair the barrel, it won't be this week though as I'm off on a short vacation.

I think what happened is that the bearing I used in the first test was slightly oversized, in fact it was harder to push into the seal than usual, and this actually jammed in the barrel, knocking it off.

Maybe you could use a copper barrel and solder it in...

You can't really solver to epoxy...

did you take the spring out in the last videos?

I put in a shorter one, because with the intended spring this was happening:

[youtube][/youtube]

Since there wasn't the pressure buildup that a barrel would have allowed, the cartridge didn't fly back hard enough and as it was trying to eject the bolt returned and jammed it against the breech.

wow im kinda wishing i was making one of those but maybe for my next gun if i feel up to it

The concept really isn't that complicated, certainly not more difficult than a bolt action

you started making any more cartridges yet?

Not before I have the breech/bolt working well and a bit of detailed power evaluation.

I'm still thinking of a smaller cartridge with a homemade check valve, perhaps with a crimped mouth to increase pop-off pressure with the same seal...

That check valve looks supsiciously like what I propose here.

jackssmirkingrevenge wrote:It has to work first not to sound pessimistic but it doesn't look like it will.

How do you plan on filling this thing, locking it in a pressurised chamber? Will there be a spring between the fill valve and the piston?

Hey, you said it, not me

FWIW, I never got that thing to work. I don't think I lost it yet, though.

ramses wrote:That check valve looks supsiciously like what I propose here.

Which also looks suspiciously like my original hybrid cartridge idea that's been floating around the forums since the spudtech days

FWIW, I never got that thing to work. I don't think I lost it yet, though.

Since I didn't see any "win!" posts on the subject I imagined my pessimism was justified

edit: I'm at charles de gaul airport with a couple of hours to kill, and needless to say I've been pondering... I think I should give the oxygen "hybrid" a go too...

Since I didn't see any "win!" posts on the subject I imagined my pessimism was justified

well now I've just GOT to make it work.


Anyway, have fun with the oxygen.

ramses wrote:Anyway, have fun with the oxygen.

I had considered the idea here, now that I have more experience with cartridges the thought of being able to bypass the filling stage and valve to have a really simple cartridge design seems to make it worth the effort, and the 5x mix that can be obtained with unpressurised oxygen should provide sufficient power for my purposes.

I should be able to knock up a working electrolysis setup in an afternoon, to provide enough oxygen for my purposes without the hazard of having a pressurised cylinder of the stuff.

Still working on this project, while the 3/8" cartridge works well it's still too big and low mix for my liking, so I've drilled out the mouth of this prototype and fitted this type of seal.

If it doesn't work I have another variation in mind, basically the same seal but inverted (with the seal "cone" opening outward) that would change the grip on the projectile and therefore pop-off pressure depending on how far you pushed it into the seal on loading.

Update: The modified seal certainly held well, even hooked up to my paintball tank at 800 psi or so the BB didn't pop, though it stuck so much out that it looked like it was just about to, which sounds good for a 16x mix. For some reason though, the schrader filling valve failed on me so I was unable to try it as a hybrid. Still, inspired enough to make a new cartridge, keep watching this space

Following POLAND_SPUD's suggestion here that it might be possible to seal a hybrid without using a seal, simply by swaging a lead projectile into the breech.

I built a quick prototype looking like this internally:



Fitting a 4.5mm lead BB in a 4mm tube, it held 20 bar without leaking. I took it to 25 bar and it didn't appear to leak but over time lost pressure.

I went on to do some hybrid testing, unfortunately I seem to have made the spark gap a little too big for high mixes. The first shot is at 5x, worked perfectly, but at 20x the spark just arcs externally.

[youtube][/youtube]

In any case, it works!

Over time, I'm sure the brass tubing would wear out and reduce pop-off pressure, but this could be compensated for by using a harder metal.

Another disadvantage is that forcing the projectile into the breech deforms it to the extent that accuracy will probably be dubious at best. I would be interesting to try with pellets instead of spherical shot.

The idea of a pellet would probably be better from several stand points.
More power due to surface area and also possibly may be able to add o-ring.

If you added more epoxy around the valve and the case lead, it may prevent the arcing. Any sharp points and the HV likes to travel to the point because it is more directional versus a circular ball shape.
Add as much epoxy as possible without interfering with the air inflation device.