3f or 2f powder for a .50 cal flintlock?

[Daryl]

  Bob.

Use whichever shoots the most accurately. Generally, you can, if you try, find a load that shoots with identical with either powders.
The load for 2F will normally be 10 to 15gr. heavier than the 3F's accuracy load. In smaller calibres, like the .40 and .45, the difference
 is usually 5 to 10gr.

[Bob Roller]

Bob,
I got my first muzzle loader in 1951 and used 3fg in it and ever since have used it in everything from
31 caliber pocket pistol to 10 gauge shotguns.The first rifle was a 58 caliber Enfield carbine I bought at
 pawn shop for $20.It still here in Huntington WV and owned by the son of the man I sold it to in 1956.
This is not high pressure powder and this nonsense of extreme loads are not reflected in guns with the
original powder measures or flasks.
Bob Roller