I launched the SPUDNIK twice yesterday morning, both times with a A10-3t engine. Both flights were stable to about 100 feet but there was corkscrewing.
The Odd'l Rockets Sputnik (with the 3" foam ball) flys vertical without any "coning" or corkscrewing.
The problem is trying to drill out a straight 1/2" hole for the engine mount tube. If the line of thrust is off by a degree or two the rocket won't fly perfectly vertical.
Add the uneven surfaces along the top and it probably won't fly without some spiraling.
Drag and weight are other considerations. On both flights the model was nose down and ejected the engine at half the altitude.
I know - MORE POWER! A larger engine (B6-2 or C6-3) would get it higher in the air but still doesn't solve the mount hole reaming and deflection from the uneven top surfaces.
The inset picture shows the micro clips connected to the igniter. If you have a Sputnik rocket, be sure the clips have no chance of getting caught up on the legs!
The Spudnik won't become a kit. There just isn't a way to ream out a straight hole for the engine mount tube.
This isn't a loss by any means. I'm only out a few dollars for the potato and two engines. You'd be surprised how many models are built, flown and not released.
I might fly it at a club launch but wouldn't want to release it for sale with the stability concerns.