kjs did a full teardown on an original Kosdon L3000 reload. The whole thing is documented on his website. Jim Rosson adds:
There were many early prototype "sledge hammer" failures due to over pressurization. According to my old Frank notes, the issue was guessed as erosivity causing the bottom grain to erode and/or collapse, and ended up blowing out the nozzle a couple of tenths into the burn time. Frank "fixed" the issue by changing the propellant formulation. There supposedly were even a few later problems with very high g (basically min diameter carbon rockets) with the final production configuration but only in high temperature (100F+) conditions.
The original L3000 "FAST" Kosdon configuration in the casing was a little strange (IMHO).
Had 4 grains, all 9"long, listed from bulkhead to nozzle:
FAST grain 31/32" core
FAST grain 31/32" core
FAST grain 1-1/16" core
SLOW grain 1-1/16" core
The nozzle throat was 0.843" nominal.
Grains were not glued to the liner.
Full diameter delay and "normal" Kosdon delay bulkhead versions were sold.
I personally would not recommend using a full diameter delay version in the L3000 for 2 reasons. 1) The high temperature failures seem to have the full diameter delay in common. 2) The original Frank nozzle had very wide/thick throat web. This large web helped to reduce nozzle erosion, and improve casing reusability due erosion; but absorbs significantly more heat flux from the motor and burning delay. The half dozen STOCK Kosdon L3000 (and the M3700 2.5" OD casing version) I saw fly with a full diameter delay all returned home with anodize darkened or burnt on the nozzle end of the casing. There were even casings melted into epoxy Glass/Carbon rockets due the this nozzle heating. I designed an improved nozzle for Kosdon East/AMW version of that casing. If you have the newer AMW nozzle design (with short ~>0.220" web throat, not the original thick <0.4" web), you will have less (but still some minor) issues with casing overheating and losing temper due the nozzle heat transfer.
Chris Pearson has the details on the 1/4" thick inhibitor ring used at the forward end of the aft two grains:
Frank used a chemical inhibitor that used MOCA (methylenebisorthochloroaniline) as a curative on some of his speciality motors, particularly the big ones. It is very toxic and is no longer made in the US. I don't know what production motors he might have used it on, if any, or when he stopped using it.
