"John" wrote:
When I was a kid in the early 70's I had a paperback book that was
called "A guide to amateur rocketry" that had plans for rockets that
used a "carmel candy" propellent based on sugar/Potassium Nitrate. You
would melt it in an oven and pour the mix into the rocket casing. The
rockets were about 4' long and describes as capable of reaching
15-20,000 ft. I think the book was written by an army captain. The
other fuel it described was a zinc/sulfur mix. I don't remember any
ISP numbers after all this time. I haven't seen the book in at least
20 years, saw it listed on bookfinder for $48

The book you are thinking of is probably "Rocket Manual for Amateurs" by
Capt. Bertrand R. Brinley; (C) 1960. (No ISBN number.) I read that book
back in the early 70's too. The copy I read went missing sometime in the
last few decades, so a year ago I managed to buy a used copy online via one
of the used book sellers who sell through Amazon.com.

Brinley did not give any ISP numbers for the "caramel candy" propellant but
did specify a theoretical ISP of 46 sec for zinc/sulfur at a chamber
pressure of 1000 PSI. However, that was after a correction factor of 50% -
the uncorrected ISP would have been 92 sec. (The stated reason for the
correction factor was because one of the exhaust products, zinc sulfide,
has a heat sublimation at the flame temperature, so that it would not
expand to produce thrust. But Brinley pointed out that at that time it
wasn't clear to what extent that happened, if at all.)