Assuming the black powder bbl. on the FX and the Encore are the same as far as length twist and bore dimensions(and i believe they are), you may want to try the Hornady SST's over about 90-95grns. of powder for starters. I prefer American Pioneer powder.
Course as you probably know, you'll have to fine tune your load to your rifle's liking.
I've not heard of anyone claiming their Prohunter will not sling the SST's accurately...
...but then again, sure as I posted that, someone will chime in with that claim.
