Incomplete burn...?

BAR here, and I've only ever flown C and smaller. This weekend I tried my first Ds, and it went GREAT! One question, though: When I took each of the engines out, I noticed two strange things: First, the top cap (that holds the ejection charge in) had not blown off completely - the charge had knocked out about 1/3 of it. Second, it looked like there was quite a bit of propellant left in the engine. Spent Bs and Cs just look like an empty tube after use; this had big chunks of black stuff on the inside. Was that unburnt powder? Should I expect higher flights if I try Ds on this rocket again?

I'm realizing a picture would be helpful, but I think I tossed the engine.

Only about half of a given mass of black powder is converted into gases; the rest remains as a solid, either in the air as smoke, or on the inside of the casing as corrosive black crud. I've had a couple motors only knock out a part of the clay cap, but the if the 'chute still deploys it's all good. It's not common, but it happens, and it's usually not a big deal. Wait 'till an E9 blows up on you; that's always exciting :wink:

Odds are the chunks are pieces of the clay cap that covers the ejection charge, if you knock a piece out and crack the chunk open it will probably be light grey inside, they are just covered in BlackPowder residue.

The delay leaves some solid residue behind. The old FSI motors left a slag that was like a used highway flare. Estes motors typically leave a charcoal-like residue, which actually helps block the nozzle when the ejection charge goes off on top.

The larger the diameter, the larger the delay and the more residue.

The residue was important to block the huge nozzle hole on the old B14 motors and it helps block the relatively large hole in the A8, B4 and D12 nozzle.