Prototype pistonless fast gun cannon

All, I post this only because I have been sitting on it with no time to work more on it for several months. if anyone is interested in toying with it, the following will get you started.

if you are not experienced, and don't already have something working DO NOT BUILD this type of cannon right now. it is a development project with all the standard caveats.

The prototype pictures below were built with only gravity feed as I have not added in the gas tube to the back of the magazine yet. it is on the to-do list but is not yet added.

Performance summary. punched clean through 1" pink foam (all I have) taking out large conical chunks on the back side. punched clean through both port and stbd. side of a big gun sheeted BB (1/8" balsa each side) from 5" range. Lighting is too poor in shop to get a chrony on it. this was all done at 110 psi.

please review operation of quick exhaust valve as the plumbing is a bit different. Port A is directly connected to gas at all times. port P is connected to a normally OPEN 3 way valve (so it is pressurized when the valve is deactivated, and depressurized when valve is activated.

Parts required:

1. one of stephen's cannon kits, specify NOT soldered together at the T or the L. (or build your own parts, for prototyping it was easier to cheat and get one of his unassembled)
2. One 1/8NPT quick exhaust valve,
3. One 1/4 compression Tee with a 1/8 NPT side male ,
4. Magnet (trial and error, 1/4OD X 1/16 thk N42 was what I used)
5. Some drill bits (3/16", 3/32, 1/16)

Fab instructions:
Drill out L with 3/16 bit in the feed in direction (purpendicular to the barrel) until when held upside down a round will get stuck in the drill dimple and block others from passing by. DO NOT DRILL THRU. should be a fairly smooth surface when done not chattery.
Drill out at the center of the 3/16" drilled hole to either 1/16 or 3/32 (I did 3/32 but I think 1/16 would be better)
bond in a blockage so the rounds can't run into the quick exhaust valve. I used a smaller diameter tube and some loctite for the time being. I plan to use the port to connect to the back end of the magazine later
bond magnet in position shown in pictures (experiment required)

the Quick exhaust valve can be positioned below (not shown in pictures) or in line with the mag (as shown in pictures). both seem to work.

general theory:
(from first gas application onwards

1. gas forces rounds up into L. first round ends up stuck in newly drilled region, blocking remainder.
2. gas is shut off, rounds fall back, first round is pulled by magnet to O-ring breech
3. gas is turned on, repeats step 1 except that now everything seals and pressurizes until round at breech fires.
4. gas is shut off, repeating step 2.
5. repeat 3-4 for each round fired.

anyways, I liked how it worded but I won't have a lot of time to play with it for a while.

see pictures below

 

you can control that by the strength of the magnet. I originally doubled up the magnet and it consistently shot doubles. then I dropped a magnet and it went to singles. I think this could be better controlled by altering the depth of the counterbore for the O-ring, but I have not tried that.

 

I should also add that I think the small diameter vent hole is not 100% required. Proper valve timing should work without it, I think

 

please play away. I have not had time to work on it at all. My primary goal was to get rid of moving bits in the cannon (spring and piston). note that it does not require the quick exhaust valve. that was just convenient for testing. technically it should work if you just use an L in place of the traditional T fitting with a gas port added. Might even work with no T/L at all at the T location if you used thin walled tubing and put gas in at the end of the magazine..

 

Using this design for a spurt gun is like using an F350 to go somewhere because you have to carry a case of coke to where you're going.

 

In reality, it's way heavier and more complex than an old-school spurt gun. Probably twice the weight, since the old spurt gun is basically a tube with a magazine connection, and a fitting to screw a barrel and o-ring to.

 

although you don't have to have the quick exhaust valve or T for it to work, so you get rid of most of that excess weight

 

But then my question would be, 'what is the advantage to building one'?

 

for a spurt, yes, unless you must have 2/3 rounds per shot. I still want to work on these this winter for normal cannons just to remove the piston/spring

 

So I have had some time to play with this cannon. it fundamentally works however the L fitting can not be brass, too soft. the gas dump from the QEV is so high that the round will eventually deform/ maybe punch through the drilled out brass fitting.

an undrilled fitting doesn't seem to suffer the same fate but I have not yet got the tuning right. so far with no piston and an undrilled L fitting, I was getting about 40 trigger pulls for 50 rounds, meaning that it doubled every so often. I think it is an indication that my accumulator is too large, but I need to finish the plumbing to find out. I need to go get a bunch of pipe fittings to play with accumulator volume.

Now on the good side, at ~135-145 psi, it was punching through 2x 1" layers of pink foam, two layers of cardboard behind the foam, and still was a significant ricochet hazard.

pictures to come later

 

It just kept destroying the hardware the qev dumped so much gas initially that I was breaking the fitting at the end of the magazine too.live with the 3D printed guns is really no point at this point other than the fact that I could practically punch through thinner fiberglass , which is too fast