SpudFiles

Hi,
I have two cannons- a standard hairspray one and a air powered one.
I have been looking around on this forum and have learned a few things but I need some help.
I want to build a propane cannon. I found a video on how to build a propane meter and found a topic on a nice one here:
http://www.spudfiles.com/forums/not-all ... 22298.html

Some questions-
what is the correct chamber to barrel ratio? I've heard .8:1 and 1.5.
Are rifled barrels worth it?
How stun gun ignition what is a good voltage?
How are dual ignition setups set up? any plans somewhere?
what is MAPP gas? Can it be run on a setup like the above one?
Are muzzle breaks worth it? Can you have a muzzle break that is sharpened to cut the potato too?

Also, I have been drawing up plans for a AT4 missile launcher type cannon with a 1.5 or 2 inch barrel inside a 3 inch pipe. The barrel would end halfway through the pipe or slightly off to get correct ratio of chamber to barrel. To hold the barrel in place i was thinking of making donuts out of wood to hold the barrel in the center and drill them in on the outside. At the end of the barrel would be a donut with the hole matching the inside diameter of the barrel so it stays in place. Would this stand up to hairspray or maybe later hold up to propane?

Finally, I am a big airsofter and to load some propane powered guns we use these. just thread them into the pipe.
http://www.airsoftpost.com/product_info ... s_id=33808
and have an adapter to go on to a regular propane tank to fill.
http://www.airsoftpost.com/product_info ... s_id=28087
but I was thinking getting the right pressure could be a problem.

Thank you very much!
Dave

Welcome to spudfiles

I suggest you have a browse through the Wiki article first as that will probably answer most of your questions.

Some questions-
what is the correct chamber to barrel ratio? I've heard .8:1 and 1.5.
Depends a bit on what you want. For most spudders a 1.5 ratio is good and will outperform an 0.8 ratio. (Though the 0.8 is more efficient.)

Are rifled barrels worth it?
Depends. Do you actually want to hit a target more than a few tens of feet from the gun? To hit a 12" square target at say 100 feet will almost certainly require a rifled barrel (or an aerodynamically stable round).

How stun gun ignition what is a good voltage?
Voltage doesn't matter, 20KV, 50KV, 200KV will all work the same. The voltage ratings are generally mostly manufacturer hype anyway and a typical stun gun's voltage will start to drop as it is used. Even that doesn't matter though since anything over 5 KV is all that is needed.

How are dual ignition setups set up? any plans somewhere?
Should be one in the spud wiki



what is MAPP gas? Can it be run on a setup like the above one?
IIRC, a mixture of propane and propadiene. Has a slightly higher energy content than propane but unless you are going for that last 10% of performance it is not any better than propane (or butane). It is metered just like propane. I believe the MAPP fuel ratio is 5% versus propane's 4%.

Are muzzle breaks worth it?
Depends on what you want. A muzzle break will reduce noise at the expense of a little performance.

Can you have a muzzle break that is sharpened to cut the potato too?
Hmmm, not sure if I've ever seen that done.

Edit: BTW the two most important things for getting the most out of a particular gun are (1) proper fuel ratio, which is what the meter is for (but a syringe is just as accurate and a lot cheaper) and (2) a chamber fan. Next probably comes a double beveled spud cutter (bevel both the inside and the outside of the barrel). Using MAPP versus propane will be a much smaller performance increase than these three features.

new person wants to up his game?? new person needs to do some research on his own first and show us your serious!! welcome to spudfiles!!

Thanks, you guys are a big help!
Time to start buying materials.

So, I'm starting to buy parts for my cannon and was just wondering whether to go stungun or bbq igniter for the ignition source.
1. I've heard some stun guns are good and others are crap. Any recommended models or brands?
2. How hard are they to set up? any diagrams?


Thanks,
Dave

Go stun gun. You can easily make a spark strip and avoid the difficult drilling and lining up screws through the chamber. Look in the combustion showcase for starman's triple thunder" thread and look at his spark strips. You can also click "cobra venom" in my signature to see how I made a similar spark strip. I highly recommend a stun gun, spark strip with 2 or 3 spark gaps and a chamber fan.

jimmy101 wrote:Depends on what you want. A muzzle break will reduce noise at the expense of a little performance.

If the brake is added to the muzzle and not made by porting the barrel, performance will not be negatively affected and may indeed increase slightly.

As to noise, muzzle brakes tend to amplify it, certainly for the shooter, by redirecting gasses that would otherwise have been thrown forward. A well designed muzzle brake can certainly make a dramatic difference in recoil, but few launchers are large enough to justift it.

So, I'm starting to buy parts for my cannon and was just wondering whether to go stungun or bbq igniter for the ignition source.

I think ignition is relatively unimportant as long as it works. Having a correct fuel mixture (metering and possibly a fan) is far more critical for performance. That said, a stun gun will definitely be more reliable than a piezo.

I agree with others, stun guns are great (though piezo's are fine).

Stun guns do have a couple drawbacks though;
1. Illegal in some places (though you can get one without the case so it basically becomes a high voltage power supply which is legal).
2. If you accidentally touch the wrong thing a stun guns hurts a lot more than a piezo.
3. It is so cool watching the stun gun spark that you'll want to play with it constantly. The circuitry really wasn't designed for more than some tens of seconds total usage so get two. One to have fun with (until it dies) and one to actually use on a gun.

Wiring is trivial, just get two wires with alligator clips on both ends (check RadioShack or make your own). Hook the stun gun's electrodes up to your chamber electrodes. You don't need a robust electrical connection and the clips let you move the stun gun from one launcher to another. You can of course open up the case and solder the wires, which will make the setup sturdier, but it isn't required.

We need a "fun stuff to do with a stun gun thread".
Take an old CD (or a new Justin Beiber CD) or DVD and put a couple deep radial scores in the plastic on the foil side. Hook up the stun gun with your handy alligator clips ...

On your AT4 design - wooden centering rings should handle hairspray, but for propane I'd recommend HDPE plastic instead. Post your drawings in the Advanced section - we love seeing scratch builds!