user: ### NOW ANSWER:
Question: What is Source, when Cartridge is .375 Remington Ultra Magnum?
Columns: ['Cartridge', 'Bullet weight', 'Muzzle velocity', 'Muzzle energy', 'Source']
Types: ['text', 'text', 'text', 'text', 'text']
Sample row: ['.375 Dakota', 'gr (g)', 'ft/s (m/s)', 'ft·lbf (J)', 'Dakota Arms']
SQL:

assistant: SELECT "Source" FROM "Table" WHERE "Cartridge" = '.375 Remington Ultra Magnum';