Spolette
From PyroGuide
A spolette is a simple type of fuse. It is made by a simple paper tube containing rammed black powder. Spolettes are often used as substitutes for time fuse and are commonly employed in Italian style canister shells (as the main fuse and as delay elements between the breaks).
The more black powder rammed into the tube the more of a delay you will get (commercial meal D gives a delay of 3 seconds per inch of powder). Spolettes are usually finished off by placing some black match in the tube end which will be to the inside of the aerial shell. This is followed by gluing some paper around the tube and tying it off with string.
Its easy to make, just make/buy a strong paper tube (various sizes, depending of the purpose ), (8mm to 1,2mm internal diameter is fine, with 3mm/4mm wall is also fine, it must to be solid and strong.) the length is depending on the purpose, but a good time for the spolette is 2.5 to 4 seconds, 3 sec is good. if you don't wanna buy a tube, just get a right stick with 8mm to 1,2 cm EXTERNAL diameter (this doesn't means that you have to make a 8mm or 1,2cm tube you can make bigger, but the must is burning with a right time), continuing, just get a stick and roll a pice of kraft paper until get a ~2mm / 3mm wall, it must to be solid and strong, tape it with hot glue or paper tape, fill it with fine black powder just fill a half of the tube, it depends of the time that you want), and use the same stick to pump with a rubber hammer or other object until the black powder get totally compressed,attach 2 or 3 pieces of black match inside of the tube,until touch in the black powder inside of the tube,just in one side, and cover it with glued kraft paper in the side that you have putted the black match ( see images), also attach a piece of black match in the other side, but laterally, not inside of the tube, and fix it with a string knot. You also should search in google images and see if your spolette is similar to the images.
This is not mine : "A spolette is a tube rammed with a few inches of black powder, since its basicly a solid fuel grain, the ignition from your first break lights the end of the spolette burning for one end to the other.
I'm not sure why they are used, and I dont think they are used very much for smaller shells (they might be used for 4"+) but for a three inch you should be better off with some time fuse (which is a spolette if you think about it)
To make them you need a strong tube, fairly fine black powder, and somthing to ram/press with. And then you just put a small amount of blackpowder in your tube - you will want to ram in small increments to get a solid burn time - ram and repeat. you also will want to time your spolettes before you trust them in a shell, just put about an inch of blackpowder in and burn it, then take down the time it took to burn and if it's the right speed your good to go, if it's too fast pack a little more BP into the next one and time that, and if it's too short, don't put as much BP in the next one, as simple as that. "
ATTENTION --- This measures aren't exact! Search on internet about Spolette tubes and see the measures. And don't forget that the measures are depending of the purpose. And always make 2 or more, because you will use one to test and count the time ( 3 seconds is good), if you get a spolette burn too fast ---> more black powder, if its slow---> less BP, just keep trying until get a 3/3,5 seconds one, keep doing those ones. I think you get that.
Video
4 sec. Spolette test – 943kb- Video of a test burn of a 4 second spolette used in 4 inch cylindrical shells.
References http://www.amateurpyro.com/forums/topic/4061-multi-break-shells-and-spolettes/