we've found that crayon rockets built with good 1/8" ply for rings and fins, and a baffle system, generally weigh in about 650 grams. the trick is: don't overbuild, enough sweep on the fins to get stability, and no nose weight required. you'll get about 400' on F40-4, twice that with a G64-7. love those cracklin' white flames!!! of course you can't go too far wrong with H97 or H128 or H165!