The tip of the nose cone was cut off and a BT-5 was slipped in acting as a ram-jet. During boost, the forced air pushed talcum powder out of a vent at the base of the nose cone.
At this point I don't know if a B6 or C6 engine would get the model to the velocity speed needed to make the nose cone work properly.
I'm building two rockets, one will be a normal 18mm model, the other will be for 24mm engines with the ramjet nose cone.
All that is needed to make a smoking nose cone is the hollow blow molded nose cone, a length of BT-5 and a 5 sized plastic nose cone.
The tip of the nose cone is cut off.
Slide the BT-5 over the tip and mark around the tube base with a pencil.
The BT-5 on the right inset picture shows more tube than needed. I cut it larger than probably needed and will cut it to size after sizing.
NOTE: The new Estes Nike Smoke nose cone has a longer shoulder than the old Centuri nose cone. I wanted the rectangular vents directly opposite the open hatch on the nose cone. I had to re-cut a new tube with the slot bottom 1 7/8" up from the bottom of the BT-5 tube.
The picture shows the slots (at the earlier 1" mark) on the BT-5 ready for cutting. Draw the slots 1 7/8" up from the bottom of the tube edge.