A few general questions, I am new at this.

[brisingre]

I am building my first combustion launcher, and the design looks like this.

3" wide 3' long pvc chamber
5' long 2" wide pvc barrel
Endcap just pulls off
PVC is, I believe, pressure rated, but I don't think the fittings are.

I am wondering
A. Is this gun going to explode
B. If so, how do I fix that
C. Otherwise, how much hairspray should I use (approximately, and I know propane is better, but this is for one of my friend's birthday and I don't have time to rig it up for propane)

Thanks in advance.

[BC Pneumatics]

brisngre, there should be a message for you in your inbox.

[Hydra]

The end cap will come off really loudly and might hit you. You better make it a screw one.

You should actually use a ball valve for venting and fueling. Add a ball valve to the end. Or shove a reducer on and a smaller ball valve.

[BigGrib]

I think you should explore this forum a little bit more and see if you can find some answers before posting. There are quite a few topics on this subject that can you can find by using the search feature. We also have a very comprehensive Wiki that will answer most of your questions. I'm not being a (expletive deleted) this is what any moderator would tell you.

[TurboSuper]

The ratio looks fine, although you're definitely going to want a threaded endcap. I'm not sure how much hairspray to spray in, that's a trial/error sort of thing.

[TwitchTheAussie]

Well thats about it. All I can add is make sure you have a decent handle, sparker and ammo. Make sure you don't point it at anyone or be an idiot with it. Also like the Eragon name of fire

[jimmy101]

I am wondering
A. Is this gun going to explode
Yes. Not a chance in hell that the end cap will stay on.
B. If so, how do I fix that
Glue on a cleanout.
C. Otherwise, how much hairspray should I use (approximately, and I know propane is better, but this is for one of my friend's birthday and I don't have time to rig it up for propane)
Use a <a href="http://www.inpharmix.com/jps/Fuel%20Met ... disposable $0.49 butane lighter and a short length of wire insulation</a>. Cheaper, easier, more effective, and cleaner than hairspray.

[pat123]

http://www.spudfiles.com/spud_wiki/inde ... ion_cannon
here is the wiiki page for combustion guns.
post some pics so we can see the pipe to make sure it is ok too use.

[CS]

While the sizes & lengths you have listed will work, I'd suggest slightly different sizes:

4" diameter chamber, 1.5' long
1.5" diameter barrel, 4' long

After about my third basic combustion I started making my cannons to these rough dimensions. I like the 1.5" barrel over the 2" barrel because most potatoes will fit, and I seem to get longer range out of it. As well I prefer the 4" chamber over the 3" chamber because you get more chamber space in a shorter length.

Then for the end your going to want a female adapter with a threaded plug.

As to your questions:
A - The truth is mostly no. Long time memebers are hesitant to absolutely say "no" because we know in rare cases guns have exploded, but the worst thing that could happen in the case of your gun is that the cleanout cap blows off. So you gotta be careful because I have had them shatter on concrete and hit people/things.
B - Already kinda answered that.
C - For the dimensions I gave you, 1-2 seconds. For the dimensions you gave I'd guess 3 seconds, maybe 4.

[Boom_erang]

While the sizes & lengths you have listed will work, I'd suggest slightly different sizes:

4" diameter chamber, 1.5' long
1.5" diameter barrel, 4' long

That's a fairly hefty C:B ratio... 226in3 chamber vs. 85in3 barrel... or 2.7:1. I would guess your cannon makes a pretty loud bang with quite the muzzle flash!

My first gun was 18"x3" chamber and 1.5x48" barrel, yielding a 1.5:1 ratio, still makes a bit of a bang but not too bad. Definitely can send a potato a loooong way.

My second gun is 8.5"x4" chamber and 44" barrel, yielding approximately a .8:1 ratio, and it seems to work amazingly well. Very efficient and fast, and not too loud at all. The silencer helps, too. I'm using static guard with both guns, which has performance similar to propane when mixed right.

-B

[brisingre]

Ok. I have added a screw on end cap. Sorry I didn't check the wiki. Thanks for all your help, guys.