Persistenprogrammer,
Going with the minimum charge weight ilsted in standard load manuals should be safe.
The suspected conditions for overpressure SEEE (Secondary Explosion Excursion Effect) and blownup guns are various combinations of the following:
1. grossly under minimum weight charges of very slow burning or hard-to-ignite powders: IMR 4831, H4831, 4350, all ball powders, etc. WW warns not to load reduced loads when using ball type propellents.
2. underweight bullets for the powder burning rate/weight (i.e. very light bullets/very slow powders).
3. Insufficient ignition (using standard primers when magnum primers are specified).
4. Large overbore capacity cases and minimum charges.
Since IMR 4064 is a medium burning rate powder, it should be safe in minimum recommended charges for a book listed load.
Unfortunately, as thoroughly as the SEEE phenomenon has been investigated, it has not been reproduced, ON DEMAND under laboratory conditions. Some studies have come close, but it is still highly theoretical.
It is suspected that SEE blowups are due to bullets leaving the cartridge case, swaging up to throat diameter, hesitating in the chamber throat due to improper ignition of the charge, and forming a momemtary bore obstruction with resultant overpressures. Something we all want to AVOID at all costs. Very good reasons to be very careful in load development and experimentation.
HTH
John
