39 replies to this topic

[Lil_Guppy]

I currently have a virtually unlimited supply 2inch ID cardboard tubes which are thick enough for mortar use, and so I was thinking about constructing my first shells to fit these tubes. While I understand that it will be hard for me to get a symetrical break from these shells, and they may also be harder (more fiddly) to make given their small size, I prefer to start out small and work my way up. This way I can get the basics down pat, and also save on chemicals (I'm a cheap so-and-so I know). I have done a reasonable bit of reading with regards to canister shell construction, and their lift charge requirements but none of the sources covered shells of this size. I was wondering what diameter the shells should be. While I realise that generally one would use a case former that is ?inch smaller than the mortar tube to allow for pasting, spiking and wrapping, my question is does this rule apply to small shells, or are the shell/former diameters different to this rule.

Any other advice on small canister shell construction would also be greatly appreciated.

Thanks

[bernie]

That's a really good question. My first thought is for you to make a dummy shell and see how it fits in your tube. Fill it with popcorn kernals, string, paste wrap, passfire and so on. Start with a 1 1/2 " former.

There's nothing wrong with being frugal w/ supplies.

Make yourself a batch of some fast burning (well milled) spider comp and cut the stars approx. 1/4-3/8" square.

Bury your tubes at least 3/4 in the ground.

Detailed notes are invaluable.

Anybody else have any suggestions?

[BigG]

I currently have a virtually unlimited supply 2inch ID cardboard tubes which are thick enough for mortar use, and so I was thinking about constructing my first shells to fit these tubes. While I understand that it will be hard for me to get a symetrical break from these shells, and they may also be harder (more fiddly) to make given their small size, I prefer to start out small and work my way up. This way I can get the basics down pat, and also save on chemicals (I'm a cheap so-and-so I know). I have done a reasonable bit of reading with regards to canister shell construction, and their lift charge requirements but none of the sources covered shells of this size. I was wondering what diameter the shells should be. While I realise that generally one would use a case former that is ?inch smaller than the mortar tube to allow for pasting, spiking and wrapping, my question is does this rule apply to small shells, or are the shell/former diameters different to this rule.

Any other advice on small canister shell construction would also be greatly appreciated.

Thanks

IT always good to start with a few dummies, but after that –

I think 1.5inch is about right. Don’t be too worry about the quality of the break – it hard to get extremely good break from such shells. I use two turns for the casting and two turn for the outer wrap on this size of shell. Fill the shell with about half stars and half granulated BP. As for spiking – 6-8 verticals seem to give best results. You can also do 2 horizontals, but they don’t seem to improve break much.

Lift using commercial BP will be about 6-10 grams. On homemade BP we are looking at 15-25. Riced BP (The kind you make just by shavings through a screen) will require more toward the 25grams. Corned BP will require more toward the 15.

[Matt]

mongrel, ive worked my way up from 15mm!! im currently up to 2 inch, ive made a 3 inch but never got around to launching it...

Big i dissagree, i use 10g pulverone, with shotty charcoal and it puts em at a good hieght.... my mortar length is probabny longer though, im the kind of person who makes longer mortars to get away with crap BP, mine are 18.5 inches long.

10g should lift a 60-70g shell. Make a shell but use dirt (anything lighter will make a long shell causing different gravity effects) and try 10, its a good tesing ammount, helps to put a spollette in as a tracer.

There, i can only really gove details on lift because well... Im not a good shell builder.

-Matt

[BigG]

mongrel, ive worked my way up from 15mm!! im currently up to 2 inch, ive made a 3 inch but never got around to launching it...

Big i dissagree, i use 10g pulverone, with shotty charcoal and it puts em at a good hieght.... my mortar length is probabny longer though, im the kind of person who makes longer mortars to get away with crap BP, mine are 18.5 inches long.

10g should lift a 60-70g shell. Make a shell but use dirt (anything lighter will make a long shell causing different gravity effects) and try 10, its a good tesing ammount, helps to put a spollette in as a tracer.

There, i can only really gove details on lift because well... Im not a good shell builder.

-Matt

Well done. Never managed to lift to a good height using such small quantity of pulverone. My Mortar is about 15 inch. 10g of Pulverone get me about 20 meters in the air. 24g is what I require to get to the same height that I get from 6-8g commercial 2FF. If I corn the staff more properly (about 1.55 density), then I can use 15g or slightly less.

[Matt]

Mine get to about 25-30. I usually dont give them enough delay to reach that though, i like to see them break upward rather than downward (can never get good breaks)

-Matt

[BigG]

Mine get to about 25-30. I usually dont give them enough delay to reach that though, i like to see them break upward rather than downward (can never get good breaks)

-Matt

Ah okay. That explains it. I'm looking more at the 40-50 meters mark. 25 meters get my stars burning almost all the way down. I like them to finish by the time they get to the 20meter overhead region.

[Matt]

Never had that problem, though ive always used fast burning stars. Cant imagine how high your 6 inch shells break....

-Matt

[alany]

I like smaller shells to break a bit low, otherwise the effect is rather diminished.

[BigG]

About 150-180 meters. Not high enough. Recommended height for 6’’ is above 200.

I will break it higher if there are lots of spectators, but I never got to measure that.
(I also don't get to do many of those this days...)

Edited by BigG, 11 February 2004 - 11:34 AM.

[alany]

I've been using this table for my pyrosim program:

http://www.japan-fir...sics/esize.html

[Lil_Guppy]

Don?t be too worry about the quality of the break ? it hard to get extremely good break from such shells.

I actually am not really worried about perfect breaks, I'm kinda more interested in the process of creating the shell, and launching it. Besides, anything that works even slightly will bring a gleam to my eyes, as I will know that I'm on the right track I might sit down and go through the shell building process with an inert filler as suggested. If anything it will prepare me for the real thing (sort of ). I will probably settle for commercial black powder, as my ball mill is not quite complete (stupid thing!). Wish me luck

Edit: Kinda on topic, but when you buy PVC pipe, is the size (50mm, 90mm etc) the internal or external diameter of the tube.

Edited by Lil_Guppy, 11 February 2004 - 12:51 PM.

[alany]

Edit: Kinda on topic, but when you buy PVC pipe, is the size (50mm, 90mm etc) the internal or external diameter of the tube.

If that means you are going to use PVC as the mortar, don't.

You'd probably get away with it for small shells, but it is not a good habit!

[pyrodude]

DO NOT USE PVC PIPING i did once and i wish i hadnt as the shell got stuck and exploded and it sent the piping into tiny pieces

[Rhodri]

There are already posts on this site describing the best media for mortar tubes.

I think it's best if 'WE' revisit these first before loading up 'tube media' that has the propensity for harm.