SpudFiles

Whether or not it makes a difference, a small puff of smoke will be mighty impressive while it's cycling.

It would be nice if it boosted performance though I'll try and do some testing this evening.

With 0.22" pellets in a 5.5mm barrel the ether should be retained for a considerable period of time with stored cartridges, my only concern is how it would affect the solid rubber piston.

edit: tried the ether in the marker pen, no hint of combustion...

As to the cartridge, worked beautifully at 400 psi but sprung a leak at 800 so I took out the schrader and reglued it, too the opportunity to fit a thicker rubber piston and reduced the pilot volume at the same time. In the meantime I'm casting the breech-barrel setup so I can test performance and get an idea of the level of blowback force. The cartridge diameter didn't seem to expand much when pressurised, but I wrapped a single layer of tape around it before casting just in case.

A bit of an update, as you can see here the cartridge works well but when it came to trying it out in the breech there wasn't even a hint of blowback. It would still work great as a cartridge for a bolt action rifle in the vein of the Predator which Brocock made for their own carts but that is not what I'm after.

As far as I can tell the issue is to do with cartridge capacity and calibre/cartridge width ratios. I could conceivably make the same cartridge with a 3mm barrel but that calibre hardly seems worthwhile, so in that context my hopes of a "scale" rifle-sized cartridge that will work in a blowback action are unrealistic.

Next step probably is to try something larger, of similar length but around the size of a 12 gauge shotgun shell. This will not only give the air a much larger area (more than 4 times bigger) to push on, but there will be more air in the cartridge itself to keep the pressure up. Results, positive or negative, will be posted here as always, watch this space

As if things weren't complicated enough, how about a "valveless" cartridge

A valveless cartridge?
Why don't you throw in some quantum physics, just to make it even harder...

Build a valveless launcher, and a cartridge design.
After both work without flaws, you can start thinking about a valveless cartridge design.
Its always good to try something new, but I recommend that you first build a successful prototype of each mechanism before combining them all together.

Hey, it was just an idea I'm sticking to coaxials for now.

Not that coaxial cartridges are exactly a new idea either, look at this from 4 years ago! I was already thinking along those lines too.



Ah, to make it work...

What about using the compressed air from venting the piston to drive some sort of cartridge ejection?

It's a thought but in the case of the last cartridge I made the pilot volume is a mere 0.07cm³ so there's not much you can do from that.

The solution is simply a bigger cartridge, more air + more surface area.

I'm tempted to make another 3/4" cartridge though now that I have double the pressure available, screw blowback for now and make one of these, hmmm...

I say go for it. You got cartridges working, enjoy it with a good ol' double barrel sawn off.

Maybe bolt action isn't such a bad idea... I was mocking up a 7.62x51 cartridge with a schrader, basically a smaller version of what jook13 did here, hmmm...

Or even better, a straight pull "shortened assault rifle" type pistol, like the Sig 556

cool. cant wait to see it finished and shooting!

Do you know how much pressure the cartridge can hold? and how's the size compared to your original design?

Do you know how much pressure the cartridge can hold?

Should be able to hold 30-40 bar+ am I right JSR?

Jsr-

Have you tried dieselin yet?

mega_swordman wrote:Do you know how much pressure the cartridge can hold? and how's the size compared to your original design?

It should be good for 55 bar plus, same as all my other similar projects as construction is almost identical. It's slightly shorter than the 0.22" cartridge but wider so volume is actually increased. Since I made it for 3mm, this actually has a much greater chance of blowing back. The ratio between calibre area and cartridge face area for my previous prototype was around 1:3, for this one it's much higher at 1:15.

I put this one together in a hurry and got the alignment wrong, so it's not sealing. No big deal, I can easily conjure up a better one, but in the meantime I noticed another potential problem. I dropped the cartridge a couple of times from waist height on a hard floor, both the mouth of the cartridge and the filling schrader became considerably deformed, clearly something a bit more resilient is required. Back to the drawing board...

Have you tried dieseling yet?

I gave it a go in the marker gun and diethyl ether from the lab, no flash or smoke was observed...

I don’t know how much abuse the Schrader valve can take, maybe you should try and make a valve which can take alot more