I will have to edit my data slightly. My comparason was with 90 grains of 3f. The comparason was between 3f and 2f. Efficiency is an interesting point. The debate of efficiency vs performance is an interesting one. Most people use hunting loads that are not as efficient in terms of powder consumption as compared to lighter target loads. They foul more and may give questionable gains. Some compare them to the effiency of a passenger car and that of a race car. You have to burn so much fuel to get so much speed or uae hotter fuel. Some want the speed out of smaller bores becasue they feel the lower velocities are inadequate. Others like the larger bores with moderate charges becasue the bigger ball gives more confidence. Personal choices.
DP
I will expand somewhat here.
What the barrel shoots best within certain criteria is all that is really important. The RB bench shooters use really massive powder charges. But the hunter does not shoot to the distances they do in most cases.
But hunting rifles seldom need much more than 1/2 ball weight of FFFG (considering 58 or smaller) to get a flat trajectory and adequate penetration. Velocity in the RB at 100 yards is not greatly increased by more that 1/2 ball weight but some barrels may like more to shoot well.
My 66" twist 54 gives all the accuracy I can use and very good velocity with 90 gr of FFFG Swiss. I used to use 100 gr of GOEX but get as good or better velocity.
Trying to increase killing power of the smaller ball by increasing velocity will not really work since velocity falls off so fast.
Increased ball diameter will increase killing power. A 16 or 20 bore ball at 1000 fps striking velocity is a better killer than a 50 cal at 2000. So attempting to make a magnum from a 50 cal, for example, by increasing the velocity is a joke. Velocity simply flattens trajectory due to initial velocity. REMAINING velocity at 100-120 is not that much greater. Some times 300 fps added at the muzzle will translate into nothing really significant at 100-120 yards.
So it is impossible to increase the downrange power of the RB by velocity increases. They do not carry out to the ranges where the ball strikes the target unless the shot is 40-50 yards.
But even then a 54 is much better than the 50. Having shot game with the 50-54-58 I think the 54 is the best compromise of the three and think it is much better than the 50 and near as good as a 58.
Bigger bores, 62 and up, change everything. Never used a 62 but the 66 is very much different than the 54, but the ball weight is doubled, 1/2 ounce ball to 1 ounce.
Ball sizes larger than 66 are suitable for large and dangerous animals. Forsythe states that the 16 bore is about as small as anyone would use on dangerous game. He hunted in Indian. He stated that with hardened balls a short barreled (26"+-) 14 bore percussion rifle (.69) using a 15 gauge ball would penetrate an Indian Elephant's head from side to side with a 137 gr of powder, Halls #5, similar to FFG powder I think. My 66 flint with 30" gives similar velocities, 1600 fps, with 140 gr of FFG Swiss. The bigger balls seem to get more out of the powder, perhaps its the greater weight or simply the bore size don't know.
Sir William Drummond Stewart who attended several fur trade Rendezvous in the 1830s used a 20 bore rifle which he stated killed more game on less powder and lead than any rifle there. An exaggeration perhaps but then maybe not. Ruxton used a 24 bore (58) with good effect. But made no claims that it was better than American rifles other than he out shot most or all in shooting matches.
But the average British gun owner was better funded than the average American gun owner so Americans opted for the smallest effective caliber for the game to be hunted to save on ammo costs or to make it go farther when far from a source of supply.
Gotta sign off.
Dan