I've switched to 2F for all rifles, .40 cal and above. It definitely tightened up groups. My loads are:
.395 ball, .017 ticking patch, spit or L.V. lube, 55 gr 2f, in .40 cal, 40 inch long GM barrel.
.490 ball, .019 denim patch, L.V. lube, 80 gr 2f, in .50 cal, 38 inch Colerain barrel.
These loads give single hole five shot groups off a rest at 60 yards in good light (and if my eyes are workin')