"The second number on those old black powder cartridges represents the weight of the black powder charge in grains. Sometimes there is a third number, indicating the bullet weight, also in grains."
Occasionally you'll also find a fourth set of numbers, as well -- the case length in inches.
During the black powder era (just as today) some people had VERY definitive ideas about what made for a proper, accurate cartridge.
Some absolutely refused to accept a bottlenecked round, believing that the bottleneck degraded accuracy.
So, manufacturers often had two cases, or two companies both offered a similar cartridge, but one was necked, the other straight...
A good example is the .40-70 Sharps.
The necked case was 2.25 inches long, while the straight case was 2.5 inches long.
"The gift which I am sending you is called a dog, and is in fact the most precious and valuable possession of mankind" -Theodorus Gaza
Baby Jesus cries when the fat redneck doesn't have military-grade firepower.