"valveless" cartridge concept

[jackssmirkingrevenge]

good luck with the new test.

Thanks, I pretty much convinced myself that I'm not going to chicken out of semi-auto just yet

And while I wait for the cartridge to cure, POLAND_SPUD - this is graphically how I understand your hybrid design

[POLAND_SPUD]

this is graphically how I understand your hybrid design

The idea is fairly simple...

Regged down propane flows to the chameber and as soon as it reaches a a set value it actuates the 3 way, which switches the valve from feeding propane to the chamebr to feeding air). The chamebr is topped off with regged down air. At that moment the mix is ready.

When the trigger is pressed and the mix ignited the round leaves the barrel and the bolt is shot back. The valve is still feeing air into the chamber, which purges it. A few ms later it returns to the original position and feeds propane, the bolt loads new ammo and seals the chamber.

Of course the trickiest part is the right timing of the purging phase. It has to end a couple of ms before the chamber is sealed again.

[irisher]

A problem I see with that design it that it requires a solenoid DCV to be exposed to hybrid ignition and the typical solenoid DCV is just not up to this task.

[jackssmirkingrevenge]

Regged down propane flows to the chameber and as soon as it reaches a a set value it actuates the 3 way, which switches the valve from feeding propane to the chamebr to feeding air). The chamber is topped off with regged down air. At that moment the mix is ready.

When you put it like that it actually makes sense

A problem I see with that design it that it requires a solenoid DCV to be exposed to hybrid ignition and the typical solenoid DCV is just not up to this task.

Wouldn't a simple check valve solve between DCV and ignition chamber solve this?

Back to the subject of this thread, had time for a quick test before work:

[youtube][/youtube]

The crimped cartridge certainly had an effect on power, there was a perceivably longer delay before it "popped" and the BB made it easily through both sides of a soup tin. Also, with the previous cartridge and the bolt spring at the above setting, the thing had failed to eject, but now as you can see it flew out quite happily

The subsequent cartridge failed to feed though, still have to investigate why, but yes, progress what I'm curious to see is if firing will "un-crimp" the cartridge mouth or if it will retain the higher pop-off pressure.

[JDP12]

looks good... i was wondering about the cartridge crimp becoming uncrimped as well. seems like after a few firings it would happen.

[Gun Freak]

Can you increase the bolt travel any more? It looks like the next cart didn't have enough time to get down before the bolt cycled.

[jackssmirkingrevenge]

looks good... i was wondering about the cartridge crimp becoming uncrimped as well. seems like after a few firings it would happen.

I doesn't seem to have affected power over repeated firings.

Can you increase the bolt travel any more? It looks like the next cart didn't have enough time to get down before the bolt cycled.

I don't think bolt travel will solve the problem, what is needed is great bolt force on return.

I tried with a heaver lead projectile and got an interesting result, bit weird isn't it?

[youtube][/youtube]

What seems to have happened is that the projectile stopped in the barrel, which means it was blocked when the second cartridge attempted to feed into the breech, and the air pressure ejected it as well. Not the effect I was after, but certainly looks good, dakka dakka!

I think I should stop fiddling with these poncy little things and move to something bigger. In terms of C:B ratio, if you consider the cartridge volume to be the effective chamber volume, the value is a tiny 0.08 with even at 800 psi is not good enough, for both muzzle energy and cycling potential.

Using a 7.62 NATO cartridge I can up that C:B ratio to 0.5 for the same barrel length, not to mention a cartridge surface area almost 4 times larger than the current one meaning greater blowback force - plus the benefits of using actual brass as has been encouraged previously

[Gun Freak]

Hmm... perhaps the repeated fails of the second cart loading made a dent or imperfection in the breech preventing another cart from loading...

[jackssmirkingrevenge]

It seems pretty intact, the friction needed to push it in due to the o-rings is the factor though.

In any case, 7.62 NATO cartridge based version is curing as we speak, I'll see what it's like in terms of power and fucntion unrestricted by a bolt tomorrow morning and we'll go from there

[Gun Freak]

Wow, you really mean business. No time wasting with you
Well hopefully this one will work well. Can't wait to see the results.

[jackssmirkingrevenge]

Wait no further, here are the initial testing results, very promising

Power is roughly the same as my other prototype, I figure that because of the tapered cartridge, it unseals the breech moments after startring to move so air is lost out the back. On the plus side however, the effort needed to seat it completely is very low, meaning there's a greater chance of chambering a fresh cartridge successfully.

Some 1000 frame per second testing, here it is with a steel BB and no restrictions at the breech:

[youtube][/youtube]

Again with a steel BB, though this time with a marker pen as a bolt, and rubber bands to keep it in place. As the rubber bands are skewed, they flip the bolt out on firing:

[youtube][/youtube]

Steel BB and double the amount of rubber bands, this time the bolt doesn't make it out of the breech but there's enough force to snap one of the bands. What's significant is that there was enough bolt delay to allow a new cartridge to be chambered were it fitted with a magazine, and the botl had more than enough force to hammer the cartridge into the breech:

[youtube][/youtube]

Some further tests:

No. 1 - steel BB with 2 skewed rubber bands at 420 frames per second

No. 2 - steel BB with 2 counter supported rubber bands at 420 frames per second

No. 3 - lead ball with 2 counter supported rubber bands at 420 frames per second, this time it tears the bands and the bolt flies right out.

No. 4 - steel BB with 2 counter supported rubber bands in real time (and yes, I sometimes enjoy working with GlaDOS chastising me in the background )

[youtube][/youtube]

In view of the above, it certainly seems work building a proper bolt, ejector and magazine, hopefull I'll have that done for testing tomorrow. In the meantime, here's a detail of the current setup astride the modified cartridge:

[Gun Freak]

Looks promising, i want to see the final version.... and some flying brass Ahhhh its gonna be cool. Good work.

[Ragnarok]

I figure that because of the tapered cartridge, it unseals the breech moments after starting to move so air is lost out the back. On the plus side however, the effort needed to seat it completely is very low

There is a way of combining the benefits of both.

It'd be a more complex design, but if you built something that used short recoil operation, then the cartridge would stay in the breech, sealing it until the bolt and barrel unlock from each other. If done right, the motion of the barrel could also be used as a valve to shut off the air flow while the barrel is back - making it easier to chamber the next round.

More complex, but perhaps not to be overlooked.

[jackssmirkingrevenge]

More complex, but perhaps not to be overlooked.

I can see it working, but in my view overly complex for what I want to achieve.

Here's the current setup with bolt and ghetto mag fitted, to be tested tomorrow.

[Ragnarok]

Well, if you're only looking for a few holes in a fairly modest target and some brass flying off, then what you've got will suffice.

But if you want to up the power with a tapered cartridge, you're going to need to stop air leaking past as it ejects, so direct blowback is no longer really an option.

See how it goes. If it lacks the desired power, you'll either need a straight walled cartridge or a more sophisticated solution to tapered carts.