This section is from the book "The Boy Mechanic Vol. 2 1000 Things for Boys to Do", by Popular Mechanics Co.. Also available from Amazon: The Boy Mechanic, Vol2: 1000 Things for Boys to Do.
Procure two empty No. 30 gauge brass cartridge shells. Cut one shell % in. shorter than the other, then flatten and bend them as shown in the sketch. The mouthpiece should be at an angle of GO deg. File a slot, 3/16in. in width, about 1/2 in. from the end. File off the flange on the shorter shell so that it will fit snugly against the side of the other and solder them together. A ring may be soldered on the end of the long shell to fasten it on a chain or string. To give the whistle a shrill sound place a large shot in each shell before flattening them. - Contributed by Peter Veneman, Paterson, New Jersey.
Ill: The Tapering End of a Cartridge Shell is Flattened And Bent to Make a Whistle