I did a marathon shoot earlier this afternoon with the 1 1/2" Thump-It mold and have a couple more things to share.
The mold likes plastic in the 330-340 range. Hotter does ok but you have to slow down the injection speed quite a bit.
When I say marathon I meant it. I did over 250 baits [5 per shot, you do the math] for tail stock. The shooting was repetitive to the max. I was only at it for an hour and a half. Yup, the mold was HOT when I wrapped it up.
I couldn't see any difference in the baits between a super hot mold or a cold one. Jerry was right about using two clamps. Right at the end I did find a couple baits with some shrinkage dimples in them but since they were going into the tail pile I paid no mind to the spots. Had I been shooting them for fishing I'd have still strung them on a jig, if that tells you how insignificant they were.
All in all I have yet to find anything of consequence in the two Thump It molds. I need to shoot another 800 or so small baits to have enough tails on hand for box filling and then it'll be on to the 2 1/2" version to do the same power shooting for tails.