I've posted a bit of the thermochemical analysis for Rapier propellant, in the original formulation by Dr Zigmund, with AP, Zn, epoxy/bakelite, DICY: the theoretical Isp is at the bottom of the page, around 107 seconds -- not far from high-quality black powder, a la Estes.
I've been surgically dissecting original Rapier units, taking careful (reverse-) engineering notes and dimensions that I'll post publicly when complete. Thanks especially to Jay Criswell for generously donating several vintage cartons of L-1, L-2, L-2 HP, L-2 LT, L-3 "Classic," L-3 [unknown batches, lots, dates], and L-4.
On careful examination, it's apparent that these motors were loaded and compressed in 6 parts: nozzle, propellant (4 loads), and end plug. The Czech grains are hard, solid, dense, well-compressed, heavy, uniform, and loaded and pressed in four portions, which has led me to several thoughts.
In my current experiments at Jetex Propulsion Lab (JPL-Mojave), I've observed that's it's simple to vary propellant compositions *within* a single, end-burning grain. I load test motors from a small poly bowl, using a large-bore plastic soda straw sliced to a sharp bias, making a simple scoop. A "full load" on the straw-scoop is about a gram of loose Rapier propellant. Ordinarily I load to scoops, then compress the grain under about 8,000-10,000 with a bench arbor press, using a spent, empty .223 Remington brass cartridge as a drift pin, along with a dowel of hardwood.
It's easy to load a Rapier motor case with two, three, or even four propellant compositions. Instances might include:
++ 1/4-grain length of faster-burning propellant, followed by 3/4-grain length of slower, sustainer mix
++ 1/4-grain length of slower-burning propellant, followed by 3/4-grain length of faster formulation
++ 1/4-grain length of regular propellant, followed by 1/4 each with red, white, and blue colored smoke sequentially.
I invite comments, suggestions, ideas, and questions on this topic. The dye pigments I'm considering (pthalo blue, etc) are non-toxic, and only diminish performance by 8-12%.