Why ? You buy your grains from RCS . All needed info is on the RCS page about fuel specifics . It is not research to share what your grain fuel choice is , core size , KN , or expected performance. You only need to be in the research area to discuss compositions.
That might burn pretty hot and destroy the case with a 12 inch long end burn grain. I'd bury it in the ground to be honest with you. Case could melt. If nozzle fails with the end grain still burning like a flare, the heat soak (if it doesn't melt the case in two) will probably severely compromise the strength of the case.12 and 16, yes. We learn by the wisdom of others. When that is not available, you experiment.
For cripes sake man. Chalk it up as a learning experience as long-necked motors are a REALLY big challenge to get right in any diameter even with a cool burning mixture. Hang in there!Well ****.... Now I am done.