Normally on Hodgdon's site they recommend not to mix powders...
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"Life should NOT be a journey to the grave with the intention of arriving safely in an attractive and well preserved body, but rather to skid in sideways, a total wreck, screaming Yahoo, with a big smile on your face."
For the sake of brevity I would say no way unless the MFG says it's ok and this general advice goes for all powders.
Hodgden does say it is OK to duplex a small amout of FFF with Pyrodex or T7 when shooting a flintlock or picky sidelock percussion gun. This is with loose powder and the shooter reducing the charge to make up for the added primer. For example you first put a little FFF Goex down the barrel before your main charge so you get better ignition.
CAN YOU MIX 777 AND PYRODEX PELLETS
