Enigma,
Powder capacity/case size is only one component in determining performance. Comparing two cases which are roughly the same size and making the argument that they should give similar velocites is a good way to get hurt. In the comparison you're making here, the 300 Savage, though similar in size and capacity to the 30-30, operates at considerably higher pressure. Specifically, the 30-30 has a SAAMI max pressure of 38,000 CUP, while the 300 Savage runs 46,000 CUP. In PSI, that's a jump from 42,000 psi to 53,000 psi. The 300 Savage brass, and guns chambered for it are intended to withstand this sort of pressure, while the 30-30 isn't. Don't push it. To take that one step further, look at the old 38 ACP, and the 38 Super. Dimensionally, the cases are completely identical; same length, same diameter, same capacity. The performance between the two, howver, is worlds apart. Chambering and firing a 38 Super round in a gun intended for the 38 ACP will likely destroy the gun on the spot. The difference between the two is pressure, pure and simple.
The 30-30 is a fine cartridge, and does what it was intended to quite admirably. It was never intended to do what 300 Mags, the 30-06 or even the 300 Savage was meant to do. If you need that level of performance, you need a rifle chambered for one of those cartridges. But don't try to make the 30-30 into something that it's not.
