I need to make sure I get this correct- as it reads a bit odd in the above statement. Stein developed gap-staging... correct?
Hmmm I THINK you could say he invented the system of open vent holes just below the upper stage nozzle. Centuri had its "Pass Port" vented coupler around 1970 or so but that was not the same - the vent holes stayed covered until the stages started to separate.I have in front of me the first, second, forth and seventh edition of Stine's book. Somewhere in the mess I call a house I have the sixth edition and I THINK
Harry mentioned that his system was different then Centuri's and he was the first to use open vent holes, but I can't find that book! May be , as others have suggested you should contact Bill Stine.
If you can get the current edition the info on gap staging starts on page 167 - I will retype a little bit
"If the shock wave of hot combustion gases was blowing the stages apart prematurely, I reasoned that we had to get rid of the pressure of the hot combustion gases in the lower stage body tube. So I vented the lower stage body tube by by punching two 1/4 -inch-diameter holes on opposite sides of the tube just below where the noxxle of the upper stage motor would be."
" Over a period of several months I flew over 100 two-stage flights with 100 percent success in upper stage ignition. Motors were separated by as much as 12 inches"
So I think that Harry was the first to publish this technique