They sell them at hunting/outdoor recreation/fishing stores etc.. There are the gun type which use a small blasting cap (like a nail gun) to launch the explosive before it explodes, or the pen launching type ones. You can also just get the explosive charge and put your own wick in it and light them that way but that's F'ing dangerous!
"Are they illegal"... well they aren't illegal per say but these days you might get some people calling Marine Animal Protection on you if they see you launching them at Seals. We saw them out at the Sand Heads actually on Monday cruising around in a zodiac.
It's a bit of a grey area I think as there was controversy a few months ago when a commie fisherman was using them and someone reported him. It was on the news.
I have the gun launching type and like it a lot. The explosive is very loud and be warned like you say it will scare people that are close by and not expecting it.
Essentially they are like a quarter stick of dynamite. They will do a lot of damage to whatever it is they explode by.
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