Second gun, trial and success (upgraded! AGAIN)

[daxspudder]

I have some good range indications, i spent 3 hours today tracking down spuds, and have this aerial shot to show my findings, the closest ones were stuck in a chain link fence at the rear of the field behind my house, the furthest ones were at the bottom of another chain link fence, which is about 100' lower than my house, the closer ones are about 50 feet lower, but no shot had more than a 15 degree angle. there might be some on the other side of the far fence, but since i live on a military base it is heavily barb wired and i dont feel like dealing with that to find spuds...

[spudmatic]

Were these shots taken with measured propane? or were you still using spray and pray?

[daxspudder]

im currently still just spray and pray. ive shot 50+shots off my back porch, and the 5 shown are the only ones i could find, i could try to do this with propane, but will likely go far beyond the far fence, which would require a 5 mile drive to get to, and then i would have to cross through some private property...

[spudmatic]

Well then I would say not too shabby. Your best shot(that you could find) got some good distance. Any plans for an even better cannon in the near future?

[daxspudder]

All my cannons thus far have been learning experiences that will hopefully lead to better cannons. I intend to build a pneumatic next, and more combustions in the future, maybe even a hybrid. Thanks for taking an interest. Oh i took a trip to home depot tonight and I'm working on my propane metering system now, but i forgot one piece which will cripple completion...

[daxspudder]

Ive completed my transition to metered propane, and have put a good little bit of work/money into making it right. I still have to measure my chamber volume again, as well as my measuring system. Also the meter attached is crappy, and i have a new one I'm gonna put on, but i misplaced the tools i need to disassemble the components. I have tested the propane system underwater with no leaks first try at 90psi, so I shouldn't have to fill it too many times to get a good 4% in the chamber. I HAVE NOT shot it yet, and i will post about it whenever I do... here is some pics of the new build.

[THUNDERLORD]

Looks like quite an upgrade.
I would like to see a better shot of the paint on the barrel.

You mentioned: "... the black down the middle is electrical tape to hide the fan wires... gonna do something about that..."

The coolest wiring I (found) was off a payphone cord But unfortunately I threw it out cleaning up. something similar, but bigger, would be MC (metal clad) or BX wire for electrical (electrician stuff). Or the plastic stuff used on speaker wire.

Nice job 8)

[daxspudder]

The wires are double insulated, once by their own, and again together inside another sleeve, the tape just keeps them flush to the cannon. If you want to see a better shot of the barrel this is the best i have at the moment, waiting for batteries for my good camera to come in the mail...

[daxspudder]

I decided to take some volume measurements on the new barrels against the chamber, I have some really good news, the 4'x2" barrel. With a chamber volume of 294.34ci a 3.93'x2" barrel makes a perfect .8:1 C:B ratio. Now I just have to wait for payday to gas up my explorer and head out to my range, had a fight with the neighbors and my backyard is out of the question for a little while. But I have alternatives. Oh I have batteries for my better camera, so I should have some high quality pics sometime soon. Not sure, but this might be a double or triple post, but its relevant, so again, if it bothers you, you have my apologies.

[starman]

You're making some good headway on the metered propane, that's a good thing! Your meter looks big enough to require only a modest pressure, maybe 40-50 psi, to get 4%. Don't take my word for that though, do your volume calculations and get it right.

40-60 psi meter pressure is good for colder weather shooting when the pressure from the propane tank drops noticably.

Looks good. Let's see some shootin' man!

[daxspudder]

Well I did the math on the meter volume, and I only need 6.5psi for exactly 4%, as the volume of the meter is 9% of the total chamber volume... I have never seen a low psi meter, does anyone know where to get one, like one that goes 0-20psi? both of the ones I have go over 120... which means 5-10psi will be pretty hard to measure accurately... a Little help please...

[ammosmoke]

Are you sure that it wasn't 65 psi? You may have misread your calculations.

[daxspudder]

well I redid my math, and figured out I did use one wrong number, instead of my chamber volume 237.07ci I had used 296.34 (CV*1.25 used to get volume need for a .8:1 C:B ratio).
so it turns out I need to have the meter at 3.55psi... meter is 39.25ci, chamber is 237.07, 4% of 237.07 is 9.48ci.

237.07/25=9.48(needed propane for 4%)
39.25/9.48=4.14(the total number of req. propane volumes in the meter)
14.7/4.14=3.55(Pressure needed to only release req. amount)

I'd give specs for meter and chamber, but they have multiple dimensions, and would be very hard to interpret, I trust my math on the ci measurements.

Seem right? and if so, where can I find a low pressure meter

[starman]

I agree 6.5 psi sounds way too low for the meter you show in the pic. Is that 1/2" pipe and ball valves you have there? Measure the actual inside diameter of the pipe, it will be much greater than 1/2" (is actually the 3/8" pipe ID). Be sure you are using the radius and not the diameter in your calculations.

FWIW...pi*radius*radius*length = cubic whatevers

meter is 39.25ci, chamber is 237.07, 4% of 237.07 is 9.48ci.

No way that meter is 39 cubic inches. Give it another look.

[daxspudder]

Good call. Thank you, I definitely just took new measurements the right way and the meter is more like 4.5ci, so 25-30psi will do the trick nicely, thanks starman, oh and my meter will work at those pressures nicely.