Cylindrical shells are said to have been in invented in Italy, centuries ago. Hence, they are also known as 'Italian shells'. They are easier to make than round shells. The pattern of stars (or 'break') produced by a cylindrical shell tends to be somewhat less symmetrical than that of a round shell. Because of their simple construction and because there are no stars involved, salutes are often constructed as cylindrical shells. An interesting variety of the cylindrical shell is the multibreak shell, which consists of a number of cylindrical shells, stacked on top of each other and interconnected with timefuse. These produce a number of breaks at regularly timed intervals.
This page describes the construction of a small (3.5 cm) cylindrical shell. Though small these shells can still produce a nice break some 20 meters across using black powder as a burst charge. The procedure can be scaled up to make shells of larger caliber.
The materialsBurst charge. Black powder works well if your casings are sufficiently strong. Though more energetic burst charges (flash powder, whistle mix) are often recommended for small shells, I find it is possible to obtain very satisfactory results using just black powder, and it is much safer to work with. Also, flash powder can disturb color perception if the flash is too bright. Ofcourse, if you use stars that are based on a chlorate composition (which is strongly discouraged for beginners) black powder burst should never be used as it contains sulfur.
Stars. Round or cylindrical (pumped/pressed) stars are best. Cut stars can be used just as well, but round or cylindrical stars will allow you to arrange the stars more evenly giving a more symmetrical break. The stars can't be large: Somewhere between 5...10 mm, depending on burn rate.
Timefuse. Visco (as will be described) works well for these small shells. For larger shells, proper timefuse is better, but visco will work.
Glue. White glue or your own favourite glue for contructing the casing and hot melt to seal the fuse. You can use white glue instead of hot melt, but hot melt is easier/quicker to work with.
String. Hemp string is traditional. You can probably use any kind of strong, thin string. Nylon for instance works well too.
Casing. For a casing you will need a cardboard tube, and two cardboard end discs. You can ofcourse use premade tubes, but it is easy enough to roll your own tubes and the advantage will be that you can make them any size you like and fits your mortar tube(s). Use a dowel with a diameter of about 15 mm less than the inner diameter of your mortar tube. The extra space is for casing thickness, string and some extra to make sure the shell doesn't fit too tightly in the mortar. The tube should be 2 to 3 times long as it is wide. For a 2.5 cm diameter dowel, Keep rolling untill you have a wall thickness of about 2 mm.
Once the stringing is done, write on the shell what's inside so that you won't forget if you make several.
Launching the shell
You will need a mortar that is a few mm wider than the shell. There must be 3 to 4 mm extra space between the mortar wall and the shell on both sides. Also, to reduce the amount of work of making a shell I ommited the lift bag/cup that is often used with larger shells. Instead, I use 4 cm diameter HDPE mortars with a fuse hole in the side and simply dump 3 to 4 grams of black powder in the mouth of the mortar, followed by the shell. This works fine. Of course, reloading the mortar must be done cautisouly as glowing embers may ignite the black powder lift charge when you dump it in the mortar. Don't have any loose shells nearby, or keep them well covered from any sparks. Don't hold any body parts over the mortar when you (re)load it.