I doubt that you could get a sound bottle to explode if you bottle within .010 of final gravity. If I thought bottles were too pressurised, I would slightly release the crown cap, and when they stopped fizzing fit new crown caps, decanting so that each bottle was filled properly. The pressure actually stops the CO2 formation process so it is self limiting. I repeat what I have said here before, it is possible to judge by eye alone when it is right to bottle, my present brew is on day 3, and I expect to bottle on day 5. Yes, the PET bottle is a safety device, a pressure indicatopr for the batch.