Lift charge, how much?

[Ubehage]

First of, I am sorry if this has already been covered in another thread. I have searched, but did not find anything..

 

When making shells, is there any 'golden rule' as to how much lift you need for different shells.

For example a 3" shell that weighs 113 grams, how much liftcharge would that need? And how do you calculate it?

[ddewees]

One ounce per pound for the first ten pounds, then half ounce per pound after that has worked well for me. A lot depends on your bp though.

 

If working in grams, just multiply your shell weight by 0.0625, then round up to the nearest gram.

 

Others may do things differently though.

Edited October 14, 2014 by ddewees

[dagabu]

Thats really considered the norm for most, commercial BP is the base for that scale.

[alexpyro101]

I've been using 10%of the shell weight for years, but i do think my shells tend to go a little too high.

[Ubehage]

Many thanks

[Mumbles]

It will take a little personal experience to get it right. The ounce per pound thing is really for slightly heavier shells, or has a rounding assumption built in. 10% is really best for lighter shells. For me personally, I do a little bit of both. I use about 10% of 4FA up to a pound, and an ounce per pound, rounded up to the next pound or half pound after that. I've had problems using 2FA in shells lighter than a pound or so.

[taiwanluthiers]

It depends a lot on granulation of your black powder, how tightly the shell fits, etc.

 

I had problem with underlifting using 2FA even using about 33g of bp in a 3" shell. I switched to 3FA and it helped.

[ddewees]

I remember when I first started, and not knowing how much (or what) to use. I decided on 50g of goex meal d to lift 4" shells. I came up with that number because that's how much fit in a small Dixie cup.

 

I think I enjoyed the lift more than the break... it was almost ground shaking. Those hdpe tubes handled it though... good times.

[Arthur]

75g lifts a kilo of a 6" shell to a good height. nb My 6" shells fit the mortar snugly. Remember that the lift needed depends on the mass of the shell and it's fit in the mortar.

 

Lift and burst height are features of your design, start with too much lift and reduce it til you get a safe break height.

[LambentPyro]

In general, the larger the grain size, the more powder you will need. 4FA powder burns much hotter than 2FA powder. The reason my powder was inconsistent because it was granulated through a 4-Mesh screen but never sifted and sized.

 

4FA powder I would say use 15 grams or so for 113 grams, that should get it up there. If you're using 2FA, use about 18-20.

[Ubehage]

I just fired the shell, using 12 grams. It went to the desired height - big success

But, the break failed. It just fizzled out. Back to the drawing board!

[schroedinger]

I just fired the shell, using 12 grams. It went to the desired height - big success

But, the break failed. It just fizzled out. Back to the drawing board!

Make a video of how you build your shell and if it again doesn't work post it so we can help you with that.

[pyroMIKE]

I just fired the shell, using 12 grams. It went to the desired height - big success

But, the break failed. It just fizzled out. Back to the drawing board!

Replace your time fuse..I had the same problem.Repalced my time fuse with some thick core Chinese time fuse, problem gone.I use the razor bade, splitting the fuse down the middle to the desired point then use a couple stands of black match in the middle tied off.Heres a pic.http://i288.photobucket.com/albums/ll194/mkillian_2008/photobucket-16197-1402416865043_zps8f56b79d.jpg

[ddewees]

Wow, look at that pasting job... looks professional.

[pyroMIKE]

Wow, look at that pasting job... looks professional.

Yeah It takes me forever to paste one..LOL..I don't skimp anywhere making shells.Takes me about 4 hours to paste a 6in by hand!

Edited October 15, 2014 by pyroMIKE

[ddewees]

Nice work.

[LambentPyro]

I know a guy named Jeff who can hand paste (like that Chinese pattern in the picture above) two 8's in about 45 minutes.

[Mumbles]

Pro tip: You can be a little sloppier on most of the layers. Just take your time on the outermost layer, and no one will notice.

[MrB]

Pro tip: You can be a little sloppier on most of the layers. Just take your time on the outermost layer, and no one will notice.

But you will know, and if there is a single break that isn't perfect, you'll blame it on the pasting. ;- )

B!

[pyroMIKE]

We will know this weekend how symmetrical that shell will be. Weather has been bad last week but it looks promising this weekend hopefully.

 

http://www.amateurpyro.com/forums/topic/10132-6in-d1-glitter-w-silver-tail-teaser/

[pyroMIKE]

I forgot to mention the shell specs.On the 6in shell in the above post, I will be using 2F. The shell weight is 1325 grams and I will be using 185g of lift which is about 14-15% the weight of the shell.As others have mentioned the OD of the shell also matters(if your using the same ID mortar tube).My last 6in shell I used 18% of shell weight (2F) because the OD of the shell was a bit smaller(less layers because I wanted a softer break). Here is a vid of that one.

Edited October 15, 2014 by pyroMIKE

[ddewees]

185!? Seems like over kill to me.

[pyroMIKE]

185!? Seems like over kill to me.

The shell I just built is gonna break BIG and loud. I want it to get up there because the stars will hang for a bit. I do not think 14% the weight is overkill. My 2F is great but not the best.If you look at the above vid that shell was 18%.

[ddewees]

That shell was nice... good luck with this one.

[Arthur]

I had some 1kilo 6" shells with 160g of lift that went up into oblivion before they broke, 100kg would have been better maybe 75g would have been enough.