In terms of safety, it makes zero difference. Loaded correctly, it will be difficult to create an unsafe load.
Conventional wisdom claims FFFg burns faster than FFg. If this is true, and I have my doubts, the difference is not significant.
What IS SIGNIFICANT is how your specific breeched barrel shoots with each granulation. You can obtain page-after-page of war stories. But stories and 35 ยข will get you coffee.
I recommend you invest in two pounds of each granulation. Decide on a load and test it:
1. For accuracy.
2. If you have a chronograph, test for velocity.
3. If you have no chronograph, get a dozen yellow pages. Wrap them together with wire, or tape, or other. Saturate with water and fire your most accurate loads into the books. Keep track of what is shot where.
Then use a rod to measure penetration. If you want to, you can examine each bullet for shape/distortion.
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Each breeched barrel will yield [slightly] different results, different preferences. Regardless what other shooters experience, your rifle will be different. Test it.
