In the spirit of discussion.
Geoff Timm did pretty much what I was about to do, copying some of the excellent data from the Remington ammo tables. With great respect to Mr. Timm, I must submit that many think that the best bullet weight for the .30-30 is actually the 150 gr. The 170 is, without question, better at short ranges, but the reduced velocity DOES result in a more arced trajectory. The 150 does a good deal better at longer ranges. I suggest you might want to go to - -
http://www.remington.com/ammo/ballistics/ballistics.htm
and play with the comparison tables, plugging in all three - - the .30-30 in both 150 and 170 and the .243 in 100.
Please note, too - - All three of these loads are calculated for use in 24-inch barrels. Velocities will be significantly lower in the more commonly seen, shorter length barrels. The vast majority of .30-30s, at least for the last 60 years, have been made with 20 inch barrels.
Another factor is the sights. The vast majority of .243 rifles are outfitted with 'scope sights, making precise aiming a lot easier. And, typically, the .30-30 is seen in the form of a lever action arm, used with the factory buckhorn or semi-buckhorn open sight. The utility of the .30-30 may be vastly improved by installation of a good aperture rear sight. Marlins and later model Winchesters are easily mounted with scope sights.
If the .30-30 cartridge is used in a bolt action or single shot action with a scope, it indeed becomes a solid 200-yard proposition. If the shooter is skilled at range estimation, there is sufficient energy to stretch that a bit.
The above comments about proper choice of bullets in the .243 are crucial. I submit that while the trajectory is plenty flat enough to allow HITS at 300 yards+, the ENERGY remaining at the longer ranges has greatly diminished, and bullet performance is problematic.
MeekAndMild's post is directly on point. The ability of the shooter, using a particular rifle/sight/ammo combination, to consistently hit a 10" circle is more what dictates maximum range than a bunch of numbers on paper. Oh, and, let's stipulate, from field positions,
not just from a bench rest. My only .30-30 is a early-1950s vintage Model '94 with a 16" barrel and aperture sights. I handload and have fired some hundreds of rounds through it. It is an excellent thick cover arm, but
MY max range for sporting use is about 100 yards.
Best,
Johnny