It really isn't all that bad when the safety valve blows, more common for the seal to leak and you get a pot of throw away.
Don't be scared, go finer, tamp harder.
After finding the breaking point, grind a step or 2 coarser and tamp a little less, you will have a great cup anytime you want, at least till the humidity changes the formula. Going the opposite direction, coarser and less tamping or no tamping was my ice coffee method before finding cold brew.
Disclaimer: By tamping I mean banging the bottom of the filler basket on the counter top to compress the grounds.