You stated that you had just put in the molds that took you a long time to make, set to 50 lbs and 2 minutes later the pot blew, resin everywhere and molds junk. I have read what everyone else has written, but I have a couple of questions to try to help get to the root to keep this from happening again.
Was this the first time to use these molds? How were they made? were they full cured? I am wondering, if these were brand new molds, if there was some sort of reaction occuring between the mold and resin. Knowing how and what the molds were like would help show or rule out this possibility.
When you tightened the lid down, did you make sure the gasket area was clean and that there wasn't anything laying or setting in the sealing area? If there was something wrong in this area, then there is the possibility that there was an overstress on one or two of the clamps causing a premature failure of the rivets/clamp.
Did you happen to notice if all the clamps tightened smoothly and evenly, or was one or two harder to tighten? If there was a noticeable difference in the tightening of one or two of the clamps, this could lead to an over/under tightening of the clamp that could lead to a failure.
There was one penturner that tried to blow up one of these pots and got it to some pretty high pressures before he had hose or connection failures, but, if I remember correctly, not a pot failure. These pots are designed with a lot more than 20 pound safety factor.
It is possible to have several reasons, all combineing into this one casting episode, such as a reaction with the mold/resin, something not allowing a complete normal seating (sealing enough to allow the pressure to build, but overstressing the clamp/rivets) of the lid to the bowl, an increase in pressure due to temp change, which is not as far fetched as you might think, or overpressure due to faulty gauge(s).
Always have a safety relief valve on your pot and piping!! Remember, this is the only thing that will keep and overpressure situation from developing.
Even your hot water heaters have a safety relief valve!!