user: Question: How many  external (cm 2 ) are there for the .338 Lapua Magnum chambering?
Columns: ['Chambering', 'P1 diameter (mm)', 'A external (cm 2 )', 'P max ( bar )', 'F bolt ( kgf )', 'F bolt']
Types: ['text', 'text', 'text', 'real', 'real', 'text']
Sample row: ['5.45x39mm', '10.00', '0.7854', 3800.0, 2985.0, 'N ( lbf )']
SQL:

assistant: SELECT "A external (cm 2 )" FROM "Table" WHERE "Chambering" = '.338 Lapua Magnum';