For instance, flame shot out the sides, and the whole propellant grain burned at once, rather than burning from one end to the other.
Well, that YouTuber is back, and here's his latest attempt.
As a member of the National Association of Rocketry, I should say that, for safety, you should definitely not do this at home. Tampering with a black powder model rocket motor in this way can be very dangerous!
But, since someone has done it, at least we can all see what it looks like, and it is fascinating.
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