We have now tested a number of glass reinforced spliced-pairs of bottles. The results so far look quite promising in improving the performance of our rockets. The extra weight of the reinforcing requires an extra 30psi to compensate, but the much higher launch pressure should raise the altitude considerably.
Next we need to assemble these into a proper rocket and pressure test it for leaks.
The full update including performance simulations is available here:
The update also includes a progress build on our first MPR pyro rocket.