RE: Sequence of shimming vs nitro
I lost two plugs this weekend - one each run, on a piped ST .45 (on 5% nitro). These didn't look like the one MJD posted, but instead the element looked normal except for it was broken about half way down (or further). I'm guessing this is due to vibration as the "tune" was fairly conservative.
I could swear I saw somewhere where it talked about the way the blown element looked was an indication of pipe length, preignition, lean run, vibration, etc...