second acorn cannon

[nc527]

Ok, so about a month ago i made a cannon with a 1/2 centimeter thick steel barrel. it uses firecrackers and for that big of a cannon, a firecracker is not enough power even with wadding. so now I have just made a prototype plan for my second try at the firecracker cannon with a 1/2 in. barrel.can any1 give me help for a beginner with cannons?

[cannonmn]

Firecracker cannons are used to make noise only as far as I know.  Firecracker powder isn't suitable as a propellant for projectiles.

What do you want your cannon to do, make noise or shoot projectiles, I couldn't tell from your post.

[Graybeard]

Dunno how smart or safe it was but as a boy I made me up a cannon from a piece of water pipe. I used black cat fire crackers as the power and shot marbles as a projectile. I was able to sent them 250-300 yards with the combination. Like I say dunno how safe it was tho we never got injured from it and it definitely did work. That is my sum total of cannon firing expereince.

[GGaskill]

We try to steer people away from using pipe for cannons.  You can find the specifications for water pipe on the internet and the strongest is the smallest and it doesn't have a very high pressure rating.  As the pipe diameter gets larger, the pressure ratings get lower (under 1000 psi.)

[cannonmn]

I did a lot of unsafe things growing up; it is a miracle I still have all my fingers and both eyes actually.

The stuff they put in firecrackers is quite a bit different from blackpowder.  I'm not a chemist but it is usually a chlorate compound (oxidizer) and a fuel (finely powdered aluminum.)  It burns many times faster than 4f black powder and produces maximum pressure almost instantaneously, so it is essentially a detonation rather than a burning.  I've heard many names for this explosive compound, including pyro powder and flashpowder.  Noisy "firecrackers" did not exist until this stuff was invented sometime, I'm guessing, around 1900.  Before that, if you wanted to make a big bang, you used a cannon or thunder mug.

[Cat Whisperer]

nc527 -

WELCOME to the board!

I have blown up lots of waterpipe (ok - it's when I was a dumb (yet lucky) kid).

General rule of thumb - use blackpowder as it's lower pressure, anything else has real potential for catestrophic failure.

Steel - not cast iron pipe.  Mild steel (1018 - 1020 - 1027 etc.) is good as it handles the repeated flexing from pressure.  Alloy steels as 4130 and 4140 are good.  Other alloys tend to get brittle.

The thickness of the steel around where the powder is should be at least as thick as the inside diameter - all around and behind it too.

SMALL diameter touch hole.

CLEARANCE (called windage) around the projectile - 1/40 the diameter of the ball is a general rule of thumb.  NOTE that the ball should roll down the bore without getting caught at any point.

Take a look at the STICKIES at the top of the topic listings and you'll find lots more.

[Cannoneer]

nc527,

 I'm not sure exactly why, but I needs to know; why are you calling it an "ACORN" cannon?

[GGaskill]

nc527,
     Your plans are too unclear for us to be able to help.  Post a dimensioned drawing or sketch of what you plan to do.  The forum standard is that the chamber walls need to be the same thickness as the chamber diameter.