IIRC the 29/40-120 "hobby" system still does it the "old" way (o-ring at the forward end of the grain, in axial compression), as distinct from the newer "radial" seal used on the "RMS High Power" hardware.
-dave w
Within the 29/40-120, I recall different batches of delay liners. Some delay liners were very loose fitting into the foreward enclosure and some had a groove for the chamber flame to creep along. Both needed tape on the o.d...
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