True about working up "mouse" loads. But P. T. Kekkonen wrote of S.E.E. occurring in a .243 WCF, 80 grain bullet, and a reduced charge of then new Norma MRP. He wrote that the pressure test setup blew up - "disintegrated" - and the test was repeated. The second testing setup blew up after a few shots (pressures slightly less than normal) with the piezo gauge peaking out at its maximum, about 150,000 PSI, before breaking. He opined that the actual peak pressure could have exceeded ten times that.
THE POWDER CHARGE WAS ONLY 15 PERCENT BELOW MAXIMUM, MAXIMUM BEING A COMPRESSED LOAD!The lesson I drew is that if you go below tested starting loads you
MAY be getting into S.E.E. territory, particularly with slow powders.
Source: 
