I would not be concerned. Fg burns much slower than FFFg will, so it takes more powder to get the same velocity using Fg powder. You need to try using both powders, cleaning our rifle between shots to give you a good idea about groups, and velocity, to see which powder granulation your gun likes better.
A Lot of people on this forum use both T/C, and Lyman rifles chambered in .54, and swear by powder charges using FFFg powder.
The only folks who use Fg powder are usually shooting large bore muskets, like a Brown Bess, or a large Gauge shotgun- 10, 8 or larger! :shocked2:
For Rifles, most choose to use either FFFg or FFg powder. The only way any of us learn which powder our gun likes, is by trying both, or all three granule sizes.
I knew a good friend who worked up loads for a .62 Caliber rifle, and found that FFFg gave much more consistent groups out of that gun than did FFg, no matter what load, and combinations of components he tried. And, he spent a couple of days at the range, trying every kind of component, and ranges of powder charges to find a good load using FFg.
Another club member with a .62 caliber rifle shot great groups using FFg powder. The first even compared notes with the second man, and went back to the range to try some ideas the second man gave him- to no avail.
Barrels will tell you what they like when it comes to powders, ball diameter, and patch thickness combinations.
Don't forget to try different kinds of lubes on the patches, too. I saw a man's groups off the bench at 50 yds cut in half JUST BY changing the patch lube he was using. I had not seen that much of an improvement before, and we were both pleasantly surprised, particularly after he shot another 5-shot group with the same result.