Originally Posted by LeeR

I did a test fit of one of MPC tracker motors in a rocket with an engine hook. It seemed a bit short so I measured it. It was 69mm long. My Estes motors measure 70mm, so not a huge difference, but noticeable.

The diameter of the motors was interesting. The MPC was 18mm, the Estes 17.6mm, both fit fine in the test rocket.

The biggest difference was casing thickness. I did not measure, but I did take a picture. The Tracker had a much thinner casing. The Estes motor is a B6-6 manufactured in 2019.