When someone says a 30-30 is only good to 150 yds
First off, it's not true. 200 is more like it. 300 with LEVERevolution bullets. Well, at least for what we call deer here. There are some places where a deer is as big as what we here in the desert might call a moose.
But second, it would mean that the bullet dropped below a certain threshold, usually of energy, and there is some distance where this is true for all bullets. It could be 10 yards, it could be 1000, depending on the bullet and muzzle velocity. It could be ZERO, depending on the game. Like you wouldn't want to rely on a .22LR to kill a grizzly, from a foot in front of it.
This chart is an interesting and informative attempt to summarize the hunting usefulness of different cartridges.
http://www.chuckhawks.com/game_range_caliber.htm
Now different people have different opinions about the thresholds of energy, bullet weight, velocity, etc. that work for different game. Roy Weatherby was famous for small but VERY fast bullets, even on very large game. Elmer Keith, on the other hand, was known for handgun hunting with big but slow bullets. Both had their share of hunting success, to say the least.
So that chart doesn't tell everything that can be told, but it's a great start.
Another factor is trajectory. If you don't want to account for range when aiming, a given cartridge will only shoot "flat" enough to a given distance. Here's a table that begins to examine that:
http://www.chuckhawks.com/rifle_trajectory_table.htm
Check these pages out. Chuck Hawks may not know everything, and he has his opinions to be taken with a grain of salt, but reading some of this is worthwhile.
http://www.chuckhawks.com/index2d.rifles.htm