...#1 and #4 nestle in the hull much more efficiently, giving you much better density and more pellets.
Example...#4 is only 30% smaller than #00 but gives 21 pellets / oz compared to 9 / oz of #00. That is an increase of over 100%.
#1 is not quite as good but still better....10% smaller but 20 % more pellets per ounce
Not to nit-pick too much, but it's probably not accurate to say "#4 is only 30%" smaller." You could say that the diameter
is 30% less, but since overall size (volume), and consequently mass, are based on cubing the radius, a #4 buck ball is more than 60% smaller (and lighter) than a 00 buck ball.
Based on listed diameters of .24" for #4, .30" for #1, and .33" for 00, along with the standard density of lead...
A #4 buck ball weighs about 20.7 grains.
A #1 buck ball weighs about 40.5 grains.
An 00 buck ball weights about 53.9 grains.
Multiplied by standard pellet counts...
#4 would hold about 558.9 grains (1.28 oz) of lead ...20.7*27
#1 would hold about 648.0 grains (1.48 oz) of lead ...40.5*16
00 would hold about 485.1 grains (1.11 oz) of lead ...53.9*9
Assuming listed diameters really are accurate, there is a definite difference in the amount of lead in each shell. Whether that's good or not depends on whether a person wants more lead or less recoil.
I'm not trying to prove that one option is better than another here. Numbers of pellets and mass totals can only show so much. I just figured if we're going to throw numbers around, we should try to do so accurately.
***Maybe someone with a good scale and each type of shell could get actual weights. What I posted above is based only on specs and calculations.