Apparently the 40 gr blitzking is good, I'm just about to try them in my older 527, angry bear has had very good results with 30gr Barnes varmint grenades in his 527 which is a hornet k
If the fox has a similar mag set up to the 527 you may find mag length restricts you to shorter (soft nose/HP) bullets as the ballistic tipped rounds are too long for the mag when loaded for best velocity 1.745" being the max length I can mag load whereas hodgdon load data for 40gr tipped rounds is with a COAL of 1.85".