(Note: The in-game bullet weight of the .44 Mag is given at 300gr. I've selected the heaviest recorded weights from the tables to be as accurate as possible in the comparison.)
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Here is the difference in impact energy at muzzle, 100yds, and 200yds (Velocity in FPS/Energy in ft*lbs):
http://www.chuckhawks.com/rifle_ballistics_table2.htm
.30-30 Win. (170 FP)
- @0.0': 2200/1827
@100': 1895/1353
@200': 1619/989
- @0.0': 1580/1524
@100': 1293/1020
@200': 1093/730
Here is the difference in calculated "killing power" at 100yds using the formula from the website:
http://www.chuckhawks.com/rifle_killing_power_list.htm
.30-30 Winchester (170 grain at 2200 fps) - 25.4
.44 Remington Magnum (Rifle) (240 grain at 1760 fps) - 26.4
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Based on the numbers above and other articles circulating the web, the .30-30 Win. performs similarly to the .44 Rem. Magnum up to 100yds (91.44m). After that distance, the .30-30 Winchester's still retains enough power for deer to 200yds (182.88m). Since the performance between the two is similar IRL, the performance should be reflected in-game as well. The .30-30 lever action should be effectively a medium range version of the .44 revolver, therefore it should have it's species list expanded and it's damage calculations improved.
For those advocating "just use the .30-06 lever action" I have. It is a wonderful rifle, however, that is another point altogether that needs to be addressed. The .30-30 needs some more love!