The design and test process of my rocket motor

When I began trying to make my own rocket motor, I did not think it would end up being so difficult. Here I'll discuss the design, each test, and the improvements made. This motor is a PVC pipe packed with a fuel mixture of 65% potassium nitrate and 35% powdered sugar. Besides for that basic idea, the rest haad to be figured out with the experiments below.

Tests 1-3: In the first three tests, I had no end caps on the motor and experimented with clay and other materials to contain the pressure. I also experimented with putting an ejection charge into the motor, but that also didn't work. Regardless, all three first tests looked very similar to the video below, with the fuel breaking through any barriers and producing a lot of smoke, but virtually no power as there was no build-up of pressure inside the motor:

Test 4: For this test, I tried to make a cap using some metal that I cut and shaped. However, there were gaps, and so the flame was able to escape through these gaps, which set the entire motor on fire, as seen in the video and picture below:

Test 5: This was the first successful test, as I figured out that I could put PVC caps onto the PVC pipe. These caps leave no gaps and perfectly contain the pressure. You can see and hear how powerful this motor is: