Lead, with a copper jacketing.

That depends on what temperature-rise you'll accept, and on what type of coating

or jacketing surrounds the cable, and on the airflow around the cable.

Total Metal Jacketed Flat Point. Many "jacketed" bullets have some lead exposed- usually at the base. TMJ wraps all of the bullet in jacketing metal. This can reduce leading of barrels, and airborne lead (indoor shooting ranges)

Would probably depend upon the gauge of the cable, the type of metal used to conduct the electricity, what kind of shielding/jacketing around the wire, and how many breaks there are in the cable i.e. crimped butt connectors if applicable.

.357 Magnum refers to the cartridge in that caliber. SOME of those cartridges are loaded with a full metal jacketed bullet- meaning that the lead core of the bullet is completely surrounded by jacketing metal- usually an alloy of copper and other metals.