Depending on length of barrel, twist, and rifling, some 45 cal guns actually do better with ffg. A friend had a long barrel with a gain twist and swore that ffg was much more accurate than fffg in that barrel. In a short barrel, 22 inches, most of the powder over 80 grains is burned up in muzzle flash. In a short barrel 2f burns sufficiently slower that there can be a marked velocity difference between 2f and 3f. In a long barrel, with charges under 80 or 90 grains velocity differences won't be as great. 2f does generally leave more fouling in the barrel. I have a long barrelled (38 inches) underhammer in 45 cal, it seems to do better with 2f. Due to weight, it is strictly a bench or cross stick gun, so for target shooting I swab the barrel between shots anyway.
If your the type of guy that wants to shoot strings of five shots without cleaning, the ffg is likely to crimp your shooting style. In a short barrel gun, your ball/bullet will probably hit a bit low. In a long barrel, there may be no difference.
