I recently got back into shooting percussion revolvers after a 30 year hiatus. During the intervening years, I did own and shoot BP rifles, though not extensively. Last year an acquaintance came into a deal on a large amount of reloading equipment and supplies as part of an estate sale. This guy is not a reloader and basically gave the stuff away for little-to-nothing. Unfortunately, he didn't approach me until he'd already sold most of it...but he still had all the powder! There was about 40 pounds of it!!!
This stuff was all over the board, including both opened and sealed cans of various pistol and rifle powders and several cans of FFg GOEX and Pyrodex RS. All of this powder was 20+ years old. There was waaaay too much for me to use, so I called several buddies and we split it up. I was already in good shape for smokeless so I didn't keep much of that, but I did keep all of the FFg and Pyrodex.
Fast forward several months later and I acquired a nice, steel-frame 1858 Remington repro. In the past, I'd always shot FFFg in revolvers, but now all I had was some of my FFg rifle powder and all of this new-to-me old GOEX FFg. I already knew that it was safe to shoot FFg in a .44 revolver, but I had never done it before.
I stuffed the Remington with 30 grain charges of both my newer FFg and the 20+ year-old GOEX and spent an enjoyable afternoon creating clouds of smoke and sending .454 balls down range!
The bottom line was that the old GOEX performed just as well as my newer FFg (which was expected, as BP doesn't deteriorate with age) and I experienced no hang or misfires using new CCI caps. Unfortunately I didn't (and still don't) have any FFFg to do a side-by-side comparison, but the FFg seemed to perform flawlessly and (admittedly going on memory, here) seemed to shoot as well or close to as well as the FFFg I'd used years previously. I haven't tried the old Pyrodex RS yet, but that'll be next on the testing agenda.
There may be more performance issues trying to use FFg in a smaller .36 BP revolver, but the big .44 Remington digested it just fine.