Film canister Shell For Mortars or Rockets This is a rough and by no means full description of the making of a simple, quick but yet interesting piece of fireworks. I first heard about it in 1994, when I visited ************** in ****************. As far as I know , this is his invention, but I guess there are some other pyros having wondered what to do with all those empty film cannisters as well. My experience with the film cannister shells is not over yet, and nor have I tried all of my ideas when it comes to payload/construction. What I will tell you now is only what you need to know to get started, the rest is up to you. I can only wish you a safe and enjoyable expansion of your fireworks items. Have fun!! ..................................................................... As with almost every fireworks item, people have their favorite materials and methods. My favorite film cannister is the black HDPE type of cannister, the type that KODAK films arrives in. What I think is the most important part is the lid. It should , in my opinion, be of the type that "squeezes" the rim of the cannister between one inner and one outer part of the lid. Here in ********, these lids are black. There are also one type of gray lid that might work, but it gets rather soft when hot glue is applied, and I have had some trouble when I tried to put it on without paying attention to the soft rim. I have also tried a few FUJI type cannisters. They are transparent, and their lids is more like a plug that does not overlap with the rim from the outside. When gluing these lids with hot glue, you get a weak seal, causing a bad break. As in all other types of shells, uniform strength is important. But carefully designing a shell using a powerful break in a flashbag is often a successful way of eliminating the effect of a weak joint. So don't loose hope if you are stuck with hundreds of FUJI type cannisters. They might work perfect with the appropriate design of the shell. The fuse used in these shells is perhaps the biggest difference from the ordinary shells. A conventional time fuse might work perfect, but it is not neccesary, and the work of cutting and priming these fuses is a waist of good pyro time. But still the fuse has to be reliable and easy to make. Visco could perhaps be used, but it is not so easy to get here. So to avoid these problems, the film cannister shell uses a special tube of black match. Instead of cotton, acryl string is used. I got my acryl in a knitting store, and if you can choose between several types, pick the thickest. Then black match is made the usual way, being sure to squeeze all the air out of the fuse, to avoid any air holes through the fuse. Dusting the finished fuse with BP is not neccesary. .......................................................... When he makes Teflon fuses, he uses a binder made from 8.5 grams of animal glue per 100 ml. of water. He also reports that household gelatin theoreticaly is the same, only more refined. He has used it as a substitute when he didn't have anything else. You have to use hot water to dissolv it. It makes a pretty good and stabile suspention of BP. .......................................................... When the black match is dry, it can be cut into pieces of about 2-2.5 cm. Then the middle part of the fuse is wrapped with Teflon tape, also known as PTFE tape. The length of the wrapping determines the timing of the shell, and has to be adjusted to the burning speed of the black match. 1.5-2 cm is a good starting point. Just be sure there is at least 2-3 mm of match on each end that is not wrapped in tape, or else a dud is on its way! The Teflon tape is soft and gives a tight seal around the match, so that no flame can spread along the surface of the fuse. Two or three layers of tape is sufficient. One roll of tape can make a lot of fuses, and the tape is easy to stretch and tear. With a little practice, it only takes a few seconds to make a fuse. Of course, if you make a lousy black match, the fuse is not as good as it could and should be. But as far as ******* ******** has experienced, it is at least as good as you could expect commercial time fuse to be. He has fired several hundreds of these shells, without any of them flower potting or failing to ignited. That should speak for itself. Depending on the diameter of your fuse, the quickest and easiest thing to do is to get some kind of punching device to punch a hole in the lid of the cannister. But as the lid is soft, anything that can make a hole is usable. However, punching gives the best hole. Then the fuse is simply just glued into the hole using hot glue, applying glue to both sides of the lid. Well, this is where every pyro has to use his own imagination. Colored stars, tailed stars, strobes, anything will do. Now you have a way to get rid of your small batches of stars, or testing small batches of stars not having to wait for the 3" shells to dry. Just remember, small shells require small stars (usually). You are on your own here. Just let the imagination flow free and undisturbed ! If you attempt to use flash, go ahead! The shell has space for 30+ grams of flash, but you might want to sacrifice some of it for some layers of craft paper on the inside walls. The film cannister is not strong enough to get the full potential out of the flash. Depending on your flash however, it is a quick way to get a salute in a hurry (don't make them if you are in a hurry!), and added titanium or zirconium makes the shell noteworthy. ................................................................ In his opinion, if you use 70:30 KP flash, reinforcement of the cannister is not neccesary. If you use nitrate based flash, you should however do something to add strength. In addition he has experimented with flash cannisters using masking tape in stead of hot glue, not because he believe there is big danger if you use hot glue, but because of the consequences if anything goes wrong. ................................................................. As in all other types of shells, the burst makes the difference between a lousy shell and a good shell (not the whole truth, but a lot of it!) And as we all have a different favorite burst, often depending on the type of stars, size and effect wanted, I will not tell you that I have found the best solution, cause I haven't! I will tell you what works for me. Due to the small size of the shell, and the relatively weak walls, a powerful burst is neccesary if you want a good spread. And I did, so I used flash burst. What flash to use, is your own choice. I have tried both perclorate flash using Dark German Al, and a milder nitrate based flash using a slower Al. They will both work if the correct amount of flash is used. I guess that whistle mix is possible to use as well, and if a milder burst is wanted, H3 or BP might give the desired effect. What I do know is that by using a powerful break, the weak joint by the lid is of no consearn. Using a softer burst especially together with the FUJI type of film cannister on the other hand, causes the lid to pop open not rupturing the cannister, creating an effect not unlike the commercial rocket heading does. This can be desirable, especially if no loud noises should be made. The more powerful burst also creates a good bang (YEAH!). So depending on your intentions, you have almost all the possibilities also found in the larger shells. The film cannister is not suited for large inserts though! Just as with traditional shells, you have different ways of arranging the burst and the stars. The far quickest method is to just fill the cannister almost full of stars, dump in a weighed or measured amount of burst (I use about 1 gram of flash), and let the flash be loose among the stars. What I have experienced is a rather weak pop and not a good spreading of the stars. Using FUJI cannisters,the several stars often came down unignited when the lid popped off. More flash, quicker flash and better priming of the stars might solve the problem. I still have to improve this method. The other method that I have used with best results is also a bit more laborous. In order to get better spread of the stars, I make a small flashbag that keeps the flash centered in the cannister. If I remember correctly, the diameter of the flashbag was about 6-7 mm, so that one gram of flash could fit into the bag. The flashbag I used was about 1 cm shorter than the length of the cannister, so that I got one layer of stars on the bottom of the cannister. I filled the flashbag with flash, and glued it onto the lid , making sure to keep it straight until the hot glue was cold. In the mean time the cannister was filled with one layer of stars on the bottom. Then a sort of "canulle" was prepared, a paper cylinder slightly wider and shorter than the flashbag consisting of two layers of paper was held in the middle of the film cannister, while the stars was filled around it. Leaving a little space for the lid on top, not filling too many stars in the cannister, the cannister in now ready to the final assembly. Now you take the glue gun, and give the lid a suitable amount of hot glue. You want the glue to touch both the outside and the inside of the cannister rim. Be aware of the theoretical danger with hot glue and stars with low ignition temperature. In practice, the glue cools down a bit before you are able to put the lid on, and it should be safe. I also wipe away all loose flash or BP that is stuck on the rim...
WMatrixie