preloaded pneumatic cartridge

[Cthulhu]

Cartridges seem to be making me more excited than they should nowadays...
What's your opinion on this Jack? It's probably a bad idea but I was thinking about those old wax dueling pistols and I was wondering how a company could make one time use disposable cartridges to fire wax bullets (that would grip rifling) for fun against other players.
I came up with this:

CascadingBurstDiskCartridge.png (7.3 KiB) Viewed 19369 times

So it's pretty weird but its just a cascading burst disk system (with permanently installed non-replaceable disks) but to make it sleek the second burst disk is shaped like a ring, with a thin tube used to fill the holding pressure before being capped with yet another burst disk which can be punctured by a firing pin to vent it and release the pressure from the main chamber.
GGDT looks promising too:

With only 300 fps it gets pretty fast velocities and has less muzzle energy than a paintball gun (if it's still too painful pressure can be lowered, decreasing it seems to drastically change velocity)

Ignoring the fact that the wax bullet pointing out would be easily deformed and the fact that most spudgunners couldn't really cheaply or easily manufacture them, do you think it could be a viable design for a company to mass produce to take advantage of the dying paintball market and growing milsim market?

[jackssmirkingrevenge]

do you think it could be a viable design for a company to mass produce to take advantage of the dying paintball market and growing milsim market?

In my experience, cartridges are a hard sell for the simulation market. Yes, they are awesome, but commercially, most customers shy away from them. They need to be individually filled, tend to be expensive per unit and are easily lost in the field.

The APS airsoft shotguns for example are about as real an experience you can get and indeed the shotgun itself is almost identical in design to the real thing, yet they are not and probably will never be as universally popular as devices using a gas reservoir for multiple shots.

For paintball the "Real Action Marker" series also failed to really take off, the shells are just another consumable to purchase which most players are looking to avoid.

[youtube][/youtube]

[null]

Hello, I'm very interested in this, could you please provide the detailed drawings?

[jackssmirkingrevenge]

Just a little preview of a cartridge I made to fit a 26.5mm flare gun, here is a rather loud first test with air only at 2500 psi:



(the noise you can hear at the end is the thousands of shattered pieces of cup flying around)

Here is the mechanism approximately to scale, it's still on the ball-locked mechanical principle but reconfigured to make it feasible at higher pressures and it's held up pretty well so far:



More testing to follow eventually.

[jackssmirkingrevenge]

A bit of fun using empty 12 gram CO2 cartridges as projectiles, not exactly hurtling at just over 200 feet per second but they pack quite a punch

[jackssmirkingrevenge]

An empty CO2 capsule averages at around 30 grams, so muzzle energy for those first tests at 2500 psi was in the 45 ft lbs range.

In the interest of ramping things up further, I "made" a better projectile by cutting down a 12g capsule to an inch in length, now weighing in at 10 grams:



At 3000 psi I got 441 fps:



That works out at 67 ft lbs, not too shabby for an "air pistol"

Normally heavier projectiles tend to generate more energy in pneumatics, but for a 20% increase in pressure I got a 55% increase in muzzle energy, with a lighter projectile.

I would surmise that one of the factors is the fact that the "cup" shape of the cut down capsule makes better use of the airflow.

[Anatine Duo]

Using the cut capsule did you fill it with something or leave it hollow? Hollow suggests dead space maybe?

Very cool air cartridge you built. Too much machining for me... remember the good old days of epoxy-cast-everything?

[jackssmirkingrevenge]

Using the cut capsule did you fill it with something or leave it hollow? Hollow suggests dead space maybe?

This is a factor, to maximize performance some sort of sabot to seal it off should help and it would be an interesting thing to compare.

Too much machining for me... remember the good old days of epoxy-cast-everything?

Ah yes, having to wait days for it to cure before testing it, only to find out that something had leaked and it's all a solid mess inside and you need to bin it and start over

Epoxy still rules for many applications but at 3000 psi in a compact package I wouldn't want to take my chances.

This thread is a little crowded so I made a separate one for this particular iteration of the preloaded pneumatic cartridge.

[jackssmirkingrevenge]

Some design studies for a 12 gauge air cartridge

[jackssmirkingrevenge]

I've done some work with a testbed cartridge for 12 gauge, here is roughly what it looks like internally:



This is just a proof of concept, the idea was to have a balanced spool (orange) within the chamber that retains pressure, in this case filled through a butane lighter type valve (brown). Because the spool diameters are balanced, it remains static. When fired, the shotgun firing pin strikes the base pin (red) that moves the piston forward, allowing air to enter behind the piston, unbalancing it and forcing it to open. The retaining rod (yellow) prevents the piston from blowing out. The front of the cartridge (green) that houses the projectile is cut from a spent 12 gauge shell.

Here is some quick testing at around 1500 psi:



It certainly works, but many elements are less than ideal.

Having the front o-ring in the path of the airflow will tend to blow it out. In my previous cartridges with the piston moving to the rear, this was not an issue.

The retaining rod takes quite a beating, I made it from brass and it started to bend from the first shot.

Just to get an idea of ballistic performance, I loaded 9 x 0.177 steel BBs, I didn't have a wad handy so I used a stack of cardboard disks instead. From the footage these obviously blew out before the BBs so naturally a lot of energy was lost but it was still promising.

Here are the component parts and the assembled cartridge:





I don't think I will develop this exact design further as there are some fundamental issues that are not feasible to solve, but it was still a reasonable and encouraging result.