I have a few different mostly stock built Estes kits. When I plug the info into the thrustcurve website, the projected heights are much less than what Estes advertises. Many times the largest recommended motor by Estes shows to be a fail on thrustcuve because of inadequate speed leaving the launch pad. For example, I am just finishing the new ESAM-58 kit sold at Hobby Lobby. The package claims 800 ft with a C6. The package does not provide a finished weight & I could not find it anywhere online, but my finished rocket weighs 89 grams ready-to-fly less motor. The kit is supplied with 1/8" launch lugs. With the typical 30" long 1/8" rod on the basic Estes launch pad the thrustcurve fails the C6 motor because the rocket would leave the pad at only 38ft/sec. I installed 3/16" lugs and have a 3/16" launch pad with a 4 ft rod. The C6 still fails with a launch speed of 43 ft/sec. Hypothetically, it would take a 6 ft rod to allow the C6 to accelerate the rocket to their recommended 50 ft/sec minimum for safe lift-off. Secondly, even with the 6 ft hypothetical rod thrustcurve calculates an altitude of 466 ft with the C6. I guessed at the drag coefficient and plugged in .75. A difference of 800 ft vs 466 ft seems pretty big to me. Even if my build was slightly heavy and my guess at the drag is off I would think it would be closer than that. Swapping the motor mount to a 24mm in thrustcurve & leaving everything else the same a D12 would reach 758 ft. Does anyone have an opinion on which would be more accurate? I launch in a small-medium sized field & like to keep launches under 1000 ft. Too high and they are lost in thick woods that surround the pasture where I launch. Too slow lift-off speed & I end up with an unstable horizontal flight that also ends up in the woods. In the ESAM-58 example above, I'm ok with using a 24mm mount & a D12 if thrustcurve is reasonably accurate, however, if Estes is correct & a C6 will send it to 800 ft I am afraid that a D12 will send it out of sight. Thoughts??