In making amateur 38mm to 98 mm motors; I never had a problem with the
basic liner. If a burn through occurred; it was at the forward bulkhead. I
eventually came up with a method that stopped it. We're talking a variety
of grain configurations, mildly AL (5% or so) APCP in 38mm to 98mm motors.
I used a variety of liner materials: EPDM, phenolic, fiberglass (my
favorite bought long ago when cheap, sigh...), Firefox graphite impregnated
cloth, etc. And lots of RTV and epoxy.
For the smaller motors (38mm and 54mm) I inserted a fiberglass end cap into
the end of the liner. This was a 1/16in thk piece of FG with a layer of the
graphite cloth epoxied on. This was then epoxied into place. These never
burnt thru in the short (5 sec or less) burns of these motors. For the 75mm
and 98 mm, there were two changes. The barriers were made of 1/8in thk FG
and there were two. One inside the liner tube; the other right on top. Once
again, both were lined with the graphite cloth and attached with epoxy. If
I used Bates grains, I RTV'ed them to the liner case. No problems at all,
no burn throughs, nada.
Just remember the basics:
Liners are cheap, rockets are expensive.
Cheers,
Brian