On Friday, December 14, 2018 at 1:15:07 PM UTC-5, wrote:
On Fri, 14 Dec 2018 09:44:30 -0800 (PST), Its Me
wrote:

it had 4 times the power (specific impulse in newton-seconds) of a military Stinger

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Are you able to calculate that in advance using knowledge of the
chemistry and rocket geometery, or do you do test firings on the
ground?

These are commercially produced motors. You can buy single use motors, or aluminum tubes and end caps, then buy the reload kits that have the propellant, O-rings, nozzles, etc for "building" the motor. They have been tested and are rated for their impulse, usually complete with graphs of how it is delivered (bell curve, big spike then slowly tapering off, etc..).

The motors are sized by the letters of the alphabet. The Low power black powder Estes motors are 1/4 and 1/2-A, A, B, C. The fat ones were D motors. E and F are considered mid power. High power starts at G and up. Each letter is a doubling of impulse range in N/s, like 2-4, 4-8, 8-16, etc... Supposedly the Stinger was in the K range. My cluster was 1 L, 2 J's and 2 I's, putting it into the M range.

Here's one source: https://www.apogeerockets.com/Rocket_Motors/Cesaroni_Propellant_Kits/54mm_Motors