Bottom Shot Construction

[Jordan]

I am making a multibreak horsetail to ringed salutes to bottom shot can shell. it is 3 inches (2.5) in diameter and I am using a plastic hemi for the bottom shot. I was wondering if it would be best to pack it full of 7/3 Kclo4 and Dark Alu. or compact 2/3 of each hemi with tissue paper and fill the middle with flash. I know that salutes with voids sometimes work better. If you have any info I'd love to hear it.

 

Thanks All, Jordan

[nater]

Have you made bottom shots like that before? Is there a reason why you are using a plastic ball shell rather than a hand rolled shot or a thick spiral wound tube? I have seen a Chinese attempt at a multi-break cylinder in which all the inserts were ball shells, however they were traditional strawboard hemis and pasting. I have heard of people trying to use plastic as inserts without any success. If it has worked for you in the past, I will stand corrected.

 

Typically bottom shots are constructed so after they are spiked and pasted, they have been built up to the nominal size of the former used on the shell. The casing for the final break is wrapped around the bottom shot as if it were a former. In a 3" shell, you can use 2.5" discs for the bottom shot and each break. It should still fit in the mortar when it is finished.

 

An alternative way of making a bottom show is to make a smaller salute and "sawdust" it in to the bottom of the shell casing. To maintain the rigidity of the shell, it is important to make sure the shot is well supported on all sides. If you were to use a ball shell, you will need to be careful that all the voids between the hemi and the cylinder shell casing are full.

 

I cannot speak for everyone, but I only leave empty spacing in salutes if they are mixed with the binary method, in which case the void in the salute is essential to it mixing. Traditional, hand rolled bottom shots need to be filled all the way full to give enough support for the shell to prevent a failure. Remember, that the bottom shot in a cylinder shell is not just a noisy effect, but part of the structure of the shells itself.

 

You might find this video helpful: http://www.fireworksnews.com/Item/D8f Do you have Pyrotechnica IX and XI aka "The Fulcanelli Papers"? That treatise goes step by step through cylinder shell from start to finish.

Edited May 26, 2014 by nater

[TYRONEEZEKIEL]

That seems very intense for one of your first shells. In shells like your case, you need the shell to be full in order for rigidity in construction. A hemi would make it difficult to spike unless you are going for a peanut shell build.

[Arthur]

Remember that the bottom takes the full pressure of the lift, whether the bottom is a disc or a shot it must not leak fire into the structure of the shell. trying to get a ball shell incorporated into the design seems fraught as any lift on the ball will only lift the cylinder at the point of contact and that force may well damage the ball or the bottom disc.

 

Make a multi without a shot until you are confident of your work, if the bottom shot goes off in the mortar then you will have mortar fragments for a large distance, you should NOT be close to the first tests

[TYRONEEZEKIEL]

Repost... Cleared Edited May 26, 2014 by TYRONEEZEKIEL

[nater]

One more thing, I started filling by filling bottom shots with BP. This let me get the construction technique solid without AS MUCH risk as flash. I don't know if a BP bottom shot would rupture a mortar or not, but if it did, it would not be as dangerous as a flash bottom shot going off in the mortar. Distance and barricades are still a must with any experimental shell.

 

I fire everything at club events, and if I am trying something new, I like to fire them when there are as few people on the B line as possible. Make sure everyone around knows what you are putting in the air and that you are still learning the construction of them. If you can, have an experienced shell builder inspect it before you drop it in the mortar. This way everyone is informed and can decide for themselves how to keep safe. If you don't have a club or experienced builder to learn from, I don't envy you. These forums are a good resource, but no match for one on one advice.

[Mumbles]

I would start with much more simple shells. Two and a half weeks ago you were asking how to test black powder for lift. Now you're trying to make complex multibreak shells while trying to make sloppy construction substitutions. Something doesn't sound right with that time frame.

 

3" multibreak shells do not require a bottom shot to function if they're made soundly. Assuming you've successfully made a few dozen single break 3" shells, I'd start with a 2 or 3 break shell containing color stars. This will give you experience in getting the proper construction and firepassing techniques down. I assure you these are things that are more difficult than they seem.

 

I also second both of Nater's book and video recommendations. They're essential for anyone wanting to learn how to make cylinder shells.

[TYRONEEZEKIEL]

Go for using the plastic hemi's I gave you as simple 3" shells. There are so many techniques that transfer from ball shells to cylinder shells, and star ignition is a great one. It took me quite some time to dial in how to get all my color comps to ignite reliably. I feel that you will have much more success and will learn more if you work in bite size chunks.

[AldoSPyro]

I am making a multibreak horsetail to ringed salutes to bottom shot can shell. it is 3 inches (2.5) in diameter and I am using a plastic hemi for the bottom shot. I was wondering if it would be best to pack it full of 7/3 Kclo4 and Dark Alu. or compact 2/3 of each hemi with tissue paper and fill the middle with flash. I know that salutes with voids sometimes work better. If you have any info I'd love to hear it.

 

Thanks All, Jordan

You should check out Pyrotechnica IX and XI, they have great papers on the construction of bottomshots and reports and canister shells.