KeystonePyro Posted June 11 Posted June 11 When people say consumer canister shells are 1.75” in diameter do they mean the inner or outer diameter
Arthur Posted June 12 Posted June 12 The nominal size of a shell is the inside diameter (bore) of the tube that the shell should be launched from. It's normal for a shell to have a small clearance to allow it to be easily loaded and to allow the leader to work properly. Expect a 2" shell to have 0.050" gap all round and a big (16") shell to have a gap of 0.200" all round. Some of the lift gas passes up the gap and lubricates the launching shell, most of the lift gas actually pushes the shell out of the tube!
Arthur Posted June 12 Posted June 12 Note that the factory may have made the shell roughly round (cylinder or ball shell) but storage and weather may change that. Card, paper and string are NOT metrology's favoured materials.
Mumbles Posted June 12 Posted June 12 I can't speak to your question with absolute certainty. It probably depends on the context and who's talking about it. I would guess they're talking about actual outer diameter of the shell itself. Consumer firework mortars come in 2 sizes most commonly. DR11 (1.91" ID) which is more common, and DR9 (1.81" ID).
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